Fighting raged for the strategic Ukrainian city Lysychansk on Saturday, as Belarusian leader Alexander Lukashenko said his army had intercepted missiles fired on his territory by Kyiv's forces.

Ukraine denied claims by Moscow-backed separatists who said they had encircled Lysychansk, the last major city in the Lugansk area of the eastern Donbas region still in Kyiv's hands.

Lysychansk is located across the river from neighbouring Severodonetsk, which Russian forces seized last week.

The city's capture would allow Russian forces to push deeper into the Donbas, which has become the focus of their offensive since failing to capture Kyiv.

"Fighting rages around Lysychansk... The city has not been encircled and is under control of the Ukrainian army," Ruslan Muzytchuk, a spokesman for the Ukrainian National Guard, said on Ukrainian television.

Earlier in the day, Andrei Marochko, a spokesman for the separatist forces, told the TASS news agency: "Lysychansk is completely encircled."

Lukashenko on Saturday accused Ukraine of "provoking" neighbouring Belarus, saying his army intercepted missiles fired at his country by Ukrainian forces "around three days ago".

The claim came one week after Ukraine said missiles struck a border region from Belarus, a long-term Russian ally that supported the February 24 invasion.

But Lukashenko denied any involvement, which would represent an escalation of the conflict. 

"As I said more than a year ago, we do not intend to fight in Ukraine," he was quoted as saying by state news agency Belta on Saturday.

- 'Heavy losses' -

Missiles continue to rain down across Ukraine, killing dozens. 

Ukrainian President Volodymyr Zelensky cited six strikes as of the evening in his daily address to the nation late Saturday.

"Fierce fighting continues along the entire front line, in Donbas," he added, noting as well that "enemy activity in the Kharkiv region is intensifying".

In the small Donetsk town of Siversk, one resident told AFP that "the bombing goes on day and night."

Rockets also struck residential properties in Sloviansk in the heart of the Donbas, killing a woman in her garden and wounding her husband, a neighbour told AFP Saturday, describing debris showered across the neighbourhood.

The witness said the strike, which took place on Friday, was thought to use cluster munitions, which spread over a large area before exploding, striking buildings and people who were outdoors.

Zelensky warned against "a feeling of relaxation" in many rear cities. 

"The war is not over," he said. "Unfortunately, its cruelty is only increasing in some places, and it cannot be forgotten."

Russian defence ministry spokesman Igor Konashenkov said Ukraine was "suffering heavy losses on all fronts", listing what he said were military targets across the country hit with artillery and missiles.

- 'Rebuilt from scratch' -

In his address, Zelensky also looked forward to a conference on Ukraine's reconstruction set to start Monday in Switzerland.

Leaders from dozens of countries and international organisations will gather in the city of Lugano with the aim of providing a roadmap for the war-ravaged country's recovery.

Rebuilding Ukraine "requires colossal investments -- billions, new technologies, best practices, new institutions and, of course, reforms," Zelensky said.

He said 10 regions of Ukraine had been affected in the war, with many towns and villages needing to be "rebuilt from scratch".

The roadmap is expected to lay out reconstruction needs in terms of damaged and destroyed infrastructure, Ukraine's devastated economy, and also environmental and social recovery needs.

The effort is expected to cost hundreds of billions of dollars.

Ukraine will also face demands for broad reforms, especially in cracking down on corruption.

The need for reforms had been underscored by European Commission, Ursula von der Leyen, who has said the coveted European Union membership was "within reach" for Ukraine, but urged Kyiv to work on anti-corruption measures.

In peacetime, Ukraine is a major agricultural exporter, but Russia's invasion has damaged farmland and seen Ukraine's ports seized, razed or blockaded -- sparking concerns about food shortages, particularly in poor countries.

Farmer Sergiy Lioubarsky, whose fields are close to the frontline, warned time was running out to harvest this year's crop. 

"We can wait until August 10 at the latest, but after that, the grains are going to dry out and fall to the ground," he said.

Western powers have accused Putin of using the trapped harvest as a weapon to increase pressure on the international community, and Russia has been accused of stealing grain.

Russia accuses Kyiv of firing missiles at Belgorod

Russia accused Kyiv on Sunday of firing three missiles at the city of Belgorod near the Ukraine border in strikes that killed at least four people.

"Russian ant-aircraft defences shot down three Tochka-U cluster missiles launched by Ukrainian nationalists against Belgorod," said Russia's defence ministry spokesman, Igor Konashenkov.

"After the destruction of the Ukrainian missiles, the debris of one of them fell on a house".

Konashenkov said that the Russian army had also shot down two Ukrainian TU-143 drones "loaded with explosives" that had been heading towards the city of Kursk, also close to the Ukrainian border.

Earlier, the governor of Belgorod, Vyachelsav Gladkov, had said that at least four people were killed and four injured in a series of "strong explosions" that rocked the city in the early hours of Sunday. 

Eleven residential buildings and 39 houses were damaged in the explosions which occurred in the early hours, he said on Telegram. 

Gladkov said he visited the site soon after the explosions, which hit five streets to the north of the city centre. 

Two of the injured -- a man and a child -- were hospitalised, while the other two were treated at the scene, he said. 

Since Moscow launched its military operation in Ukraine on February 24, Russia has repeatedly accused Kyiv of conducting strikes on Russian soil, particularly in the Belgorod region. 

At the beginning of April, Gladkov accused Ukraine of attacking a fuel depot in the city with two helicopters.