The fragile truce between Iran and the United States showed signs of unravelling on Thursday, with Tehran threatening to resume hostilities as Israel pummelled Lebanon, massacring over 250 people.
Washington and Tehran both claimed victory after agreeing to a two-week ceasefire and negotiations aimed at ending a war that has killed thousands across the Middle East and sparked global economic upheaval.
But the deal's fractures emerged quickly on Wednesday as Israel carried out its heaviest strikes on neighbouring Lebanon -- including in densely-packed central Beirut -- since the Iran-backed Hezbollah joined the war in early March.
Israeli strikes have hit several dense commercial and residential areas in central Beirut without warning, killing hundreds of people and wounding more than 1,000 others, hours after a ceasefire was announced in the United States-Israeli war on Iran.
Lebanon’s Civil Defence said at least 254 people were killed and 1,165 others were wounded in the attacks on Wednesday.
Hezbollah responded on Thursday, saying it had fired rockets towards Israel and accusing it of violating the US-Iran truce, which was agreed late Tuesday.
Israel had said earlier its battle against the Lebanese group was not part of the ceasefire, an argument echoed by US Vice President JD Vance, days before he is due to lead talks with Tehran in Pakistan.
"If Iran wants to let this negotiation fall apart...over Lebanon, which has nothing to do with them, and which the United States never once said was part of the ceasefire, that's ultimately their choice," he said.
But Iran's parliament speaker Mohammad Bagher Ghalibaf appeared to threaten the ceasefire, posting on X that the "workable basis on which to negotiate" had already been violated, making further talks "unreasonable".
Ghalibaf listed three alleged US violations of the truce plan: the continued attacks in Lebanon, a drone entering Iranian airspace, and a denial of the country's right to enrichment.
Adding to the fragility of the truce -- agreed hours before a deadline set by US President Donald Trump -- a senior US official said Iran's 10-point plan was not the same set of conditions the White House had agreed to in order to pause the war.
In Lebanon, where UN rights chief Volker Turk called the scale of killing "horrific", strikes across the capital Beirut without warning triggered scenes of horror and panic.
"People started running left and right, and smoke was billowing," said Ali Younes, who was waiting for his wife near Corniche al-Mazraa, one of the areas targeted.
More than 1,700 people have been killed in Lebanon since Israel launched airstrikes and a ground invasion last month, local officials said.
Iran's Revolutionary Guards warned they would "fulfil our duty and deliver a response" if Israel did not cease its strikes, while Hezbollah said it had a "right" to respond.
Israeli Prime Minister Benjamin Netanyahu said the country remained prepared to confront Iran if necessary, as it still had "objectives to complete", with the military saying it continued to pursue the goal of "disarming" Hezbollah in Lebanon.
Pentagon chief Pete Hegseth also vowed that American forces remained at the ready if the conflict flared up again.
- High-stakes talks -
The belligerent rhetoric came ahead of high-stakes talks in Pakistan expected on Friday or Saturday, after Iran temporarily agreed to reopen the Strait of Hormuz under threat of annihilation by Trump, with ships passing through the strategic waterway on Wednesday.
But reports suggested the waterway was shut again later in the day despite the ceasefire, something the White House called "completely unacceptable".
Iran announced alternative routes on Thursday for ships travelling through the Strait of Hormuz, citing the risk of sea mines in the main navigational zone.
Pakistani Prime Minister Shehbaz Sharif, whose country mediated the ceasefire, urged on X for all parties to "exercise restraint and respect the ceasefire for two weeks" to allow diplomacy to take hold.
Further casting doubt on the truce's durability, Iranian state media announced fresh missile and drone attacks against US-allied Gulf states in retaliation for airstrikes on its oil facilities, with Kuwait, the UAE, Saudi Arabia and Bahrain all reporting strikes since the ceasefire took effect.
In Tehran, streets were quieter than usual on Wednesday, with many shops closed after a long and anxious night for residents fearing a massive US attack.
"Everyone is at ease now," said Sakineh Mohammadi, a 50-year-old housewife, adding she was "proud" of her country.
"We are more relaxed."
- 'Won't be there' -
On Wednesday, the leaders of several European nations, Canada and the United Kingdom said "a swift and lasting end to the war" must be negotiated, as Pope Leo hailed a moment of "real hope".
But Tehran's demands over uranium enrichment, economic sanctions and future control of the Strait of Hormuz -- a narrow waterway through which one-fifth of the world's oil passes -- remain deeply at odds with those of the United States.
The United States and Israel said they attacked Iran to degrade its military capacity.
After weeks of economic turmoil, the ceasefire announcement sent oil prices plunging 15 percent, while European natural gas dropped 20 percent.
Trump meanwhile vented his anger at NATO members he believed had been unhelpful during the conflict, saying "they won't be there" for the United States.
As Trump met with NATO's chief in Washington on Wednesday, the White House said he was expected to discuss possibly leaving the alliance.
Iran announces alternative routes in Hormuz strait
Iran announced alternative routes on Thursday for ships travelling through the Strait of Hormuz, citing the risk of sea mines in the main zone of the vital waterway.
Tehran has agreed to temporarily reopen the strait, through which one-fifth of the world's oil usually passes, as part of a two-week truce.
"All ships intending to transit the Strait of Hormuz are hereby notified that in order to comply with the principles of maritime safety and to be protected from possible collisions with sea mines...they should take alternative routes for traffic in the Strait of Hormuz," Iran's Revolutionary Guards said in a statement quoted by local media.
The statement shared instructions for an alternative entry and exit route through the strait.
The United States and Iran agreed to a two-week ceasefire overnight from Tuesday to Wednesday, less than an hour before US President Donald Trump's deadline to obliterate the Islamic republic if it did not bow to his demands for a deal to reopen the Strait of Hormuz.
Tehran had effectively blocked the key shipping route since early March, sending global energy prices spiralling.
- Lebanon declares day of mourning -
Lebanese Prime Minister Nawaf Salam declared Thursday a national day of mourning after Israeli strikes pummelled the country, killing at least 182 people and wounding 890, according to the health ministry.
The strikes were Israel's heaviest on neighboring Lebanon -- including in densely packed central Beirut -- since the Iran-backed militant group Hezbollah joined the war in early March.
Spain to reopen embassy in Iran
Spain will reopen its embassy in Iran, which was closed in March due to the war, Spanish Foreign Minister Jose Manuel Albares said Thursday, following the truce reached between the United States, Israel, and Iran.
"I have given instructions to our ambassador in Tehran to return, to resume his post and reopen the Spanish embassy in Tehran, and for us to contribute through all the means available to us, including from Iran’s own capital, to efforts for peace," he told reporters in Madrid.
- Hezbollah fires at Israel -
Iran-backed militant group Hezbollah said Thursday it had fired rockets towards Israel in response to its "violation" of the US-Iran truce.
It came a day after the Lebanese group said it has a "right" to respond to a deadly wave of Israeli strikes across Lebanon.
- Israel strikes in Beirut hardest yet -
The Lebanese health ministry reported that 182 people were killed and 890 were wounded by Israeli strikes on Wednesday. The capital Beirut was hit by the most violent bombardment since the start of the war between Israel and Hezbollah.
Israel's defence minister said it had carried out an attack targeting Hezbollah members across Lebanon, calling it the largest blow against the group since a 2024 operation involving pager bombs.
- Tehran residents 'relieved' -
Some in the Iranian capital feared the ceasefire will come to naught, but others declared victory and most breathed a sigh of relief after weeks of bombardment.
"Everyone is at ease now, we are more relaxed," Sakineh Mohammadi, a 50-year-old housewife, told AFP, saying she was "proud" of her country.
- Iran demands Lebanon truce -
Pezeshkian said a halt to Israeli attacks in Lebanon was one of the key conditions of the Islamic Republic's 10-point plan for securing an end to the Middle East war, state media reported Wednesday.
His remarks came after Israel launched its largest wave of strikes against its neighbour -- including in densely packed central Beirut -- since fighting resumed against Lebanon's Iran-backed militant group Hezbollah.
The Lebanese Health Ministry said 182 people were killed and nearly 900 wounded on Wednesday, with the toll likely to rise.
- Vance to lead US delegation to Islamabad -
US Vice President JD Vance will lead talks with Iran beginning Saturday in Islamabad, and will be joined by special envoy Steve Witkoff and Trump's son-in-law Jared Kushner, the White House said.
Speaking to reporters in Hungary, Vance urged Iran not to let the truce fall apart over Lebanon, insisting that a halt to Israel's fighting there had never been a part of the agreement reached the night before.
- UN outrage over Lebanon killings -
The UN rights chief and the International Committee of the Red Cross (ICRC) voiced outrage over Israel's attacks on Lebanon.
"The scale of the killing and destruction in Lebanon today is nothing short of horrific," UN High Commissioner for Human Rights Volker Turk said. "Such carnage, within hours of agreeing to a ceasefire with Iran, defies belief."
The ICRC said it was "outraged by the devastating death and destruction."
- Israel ready to 'return to battle' -
Prime Minister Benjamin Netanyahu said Israel remained prepared to confront Iran if necessary, despite the US-Iran truce.
"Let me be clear: We still have objectives to complete, and we will achieve them -- either through agreement or through renewed fighting," Netanyahu said in a televised statement.
Attacks on Lebanon endangering US-Iran ceasefire: EU
The European Union on Thursday called on Israel to halt its strikes on Lebanon which it said were endangering the US-Iran ceasefire.
"Israeli actions are putting the US-Iran ceasefire under severe strain. The Iran truce should extend to Lebanon," the European Union's top diplomat Kaja Kallas said.
"Hezbollah dragged Lebanon into the war, but Israel’s right to defend itself does not justify inflicting such massive destruction," she said.
"Israeli strikes killed hundreds last night, making it hard to argue that such heavy-handed actions fall within self-defence," she added.
"Hezbollah must disarm, as it agreed to do. The EU supports Lebanon’s efforts to disarm" the Iran-backed group, Kallas added.