Ukraine's President Volodymyr Zelensky on Saturday criticised a decision by UN Secretary General Antonio Guterres to visit Moscow on Tuesday, before heading to Kyiv.

"It is simply wrong to go first to Russia and then to Ukraine," Zelensky told reporters in the Ukraine capital. "There is no justice and no logic in this order," he added.

"The war is in Ukraine, there are no bodies in the streets of Moscow. It would be logical to go first to Ukraine, to see the people there, the consequences of the occupation," he said.

In the Kyiv region alone, more than a 1,000 civilians had been killed, he added.

Guterres is due to meet Russian President Vladimir Putin on Tuesday, then Zelensky on Thursday.

The UN chief also plans to meet UN staff on staff to discuss stepping up aid for Ukrainians.

Since Guterres accused Russia of violating the UN charter by sending troops into Ukraine, the Russian leader has refused any contact with him.

The UN chief has had little contact with Zelensky either, apart from a telephone conversation on February 26 two days after the Russian attack began.

On Tuesday, Guterres once again denounced the Russian offensive in eastern Ukraine, calling on both sides to stop fighting and observe a four-day humanitarian truce over the Orthodox Easter, which is on Sunday.

Top US officials to visit, Odessa attack kills eight

Kyiv prepared on Saturday for its first wartime visit from two top US officials, as Ukraine accused Russia of killing eight people, including an infant, in a strike on the southern city of Odessa that all but buried hopes of a truce for Orthodox Easter. 

The Sunday visit by Secretary of State Antony Blinken and Defense Secretary Lloyd Austin will come at a symbolic moment -- on the day the war enters its third month -- and with fierce battles continuing in the country's east.

It also comes as the situation in the shattered port city of Mariupol remains bleak. The latest of many attempts to evacuate civilians failed Saturday, and the situation facing an embattled unit of Ukrainian fighters sheltering in tunnels under a sprawling steel mill there appeared increasingly desperate.

A series of European leaders have already traveled to Kyiv to meet with President Volodymyr Zelensky and underscore their support, but the United States -- a leading donor of finances and weaponry -- had yet to send any top officials.

Asked by AFP to comment on the highly sensitive trip by two of President Joe Biden's top cabinet members, the State Department declined.

Zelensky, who announced the visit, also issued a new call for a meeting with Russian counterpart Vladimir Putin "to end the war."

"I think that whoever started this war will be able to end it," Zelensky said, adding he was "not afraid" to meet the Russian leader.

But he again stressed that Kyiv would abandon talks with Moscow if its troops in Mariupol were killed.

Zelensky also criticized a decision by UN Secretary General Antonio Guterres to visit Moscow on Tuesday, before heading to Kyiv.

"There is no justice and no logic in this order," he said.

Around 200 residents gathered at a designated evacuation point in Mariupol on Saturday but were "dispersed" by Russian forces, city official Petro Andryushchenko said on Telegram, adding: "The evacuation was thwarted."

He claimed others had been told to board buses headed to places controlled by Russia. 

Mariupol, which the Kremlin claims to have "liberated", is pivotal to Russia's war plans to forge a land bridge to Russian-occupied Crimea -- and possibly beyond as far as Moldova.

Ukraine says hundreds of its forces and civilians are holed up inside the Mariupol steel plant. Kyiv has repeatedly called for a ceasefire to allow civilians -- many barely surviving with little or no access to food or water -- to exit safely.

But on Saturday a Ukrainian presidential adviser, Oleksiy Arestovich, said Russian forces had resumed air strikes on the factory.

"Our defenders hold on regardless of the very difficult situation and even carry out counter-raids," he said.

- Eight dead in Odessa -

Further west, a missile struck a residential building in the Black Sea port of Odessa, killing eight people, including a three-month-old baby, and wounding at least 18, according to Zelensky.

"It looks like killing children is Russia's new national idea," Zelensky said in his daily address to the nation, vowing to bring those responsible to justice. "All those bastards will answer for every death."

And Russia's defence ministry also said it had targeted a major depot stocking foreign weapons near Odessa, attacks that upended the relative calm the city has enjoyed since the beginning of the war. 

The ministry also charged that Ukrainian special services in Odessa were preparing a "provocation with the use of toxic chemical substances" that could then be blamed on Russia.

Western powers have accused Russia in the past of making such accusations as a cover or diversion for attacks its own forces are planning.

- 'Evacuate if you can' -

In the Lugansk region in the east, six civilians died Saturday from Russian shelling in the village of Girske, governor Sergiy Gaiday said on Telegram.

Earlier, Gaiday said shelling was "round the clock" and urged people near the front to "evacuate if you have the chance". 

The latest fighting came a day after a senior Russian military officer announced the beginning of "the second phase of the special operation."

"One of the tasks of the Russian army is to establish full control over the Donbas and southern Ukraine," Major General Rustam Minnekaev said.

Russian forces, which withdrew from around Kyiv and the north of Ukraine after being frustrated in their attempts to take the capital, already occupy much of the eastern Donbas region and the south.

Minnekaev said the focus was to "provide a land corridor to Crimea," which Russia annexed in 2014, and possibly towards Transnistria, a breakaway pro-Russian region of Moldova where the general claimed Russian-speaking people were "being oppressed".

- 'What could be worse' -

After changing their strategic focus to southern and eastern Ukraine, Russian forces left behind a trail of indiscriminate destruction around Kyiv, including in the commuter town of Bucha.

A United Nations mission to Bucha documented "the unlawful killing, including by summary execution, of some 50 civilians there", the UN's Office of the High Commissioner for Human Rights said.

Russian forces had "indiscriminately shelled and bombed populated areas, killing civilians and wrecking hospitals, schools and other civilian infrastructure, actions that may amount to war crimes".

Tania Boikiv, 52, said Russian troops took her husband from their home in Bucha, held him for two weeks, then beat him to death as they retreated.

"The most terrible thing in my life is that my husband, my loved one, is gone," she told AFP. "I don't know what could be worse."

Also Saturday, Roman Starovoit, the governor of Russia's region of Kursk, which borders Ukraine, said on Telegram that a Russian border post had been hit by Ukrainian mortar fire, although there were no casualties.

Latest developments

Here are the latest developments in the war in Ukraine:

- Fighting in the east -

Authorities in two eastern Ukrainian regions report "fierce" fighting with Russian forces as hope fades for a truce over Orthodox Easter weekend.

The governor of the eastern Kharkiv region, Oleg Sinegubov, says Kyiv retook three villages near the Russian border after "fierce battles".

- Russian gas exports -

A third of Russian gas exported to the European Union could be affected because of the war, says the head of Ukraine's state gas company Naftogaz.

"We estimate a third of the gas exported from Russia to the European Union via Ukraine will be lost if the (Russian) forces of occupation don't stop disrupting the working of the stations in the recently occupied territories," Yuriy Vitrenko writes on Twitter.

- Mariupol evacuation -

Ukrainian officials accuse Russia of having thwarted attempts to evacuate more civilians from Mariupol, the devastated port city now largely controlled by Russian forces.

- UN chief criticised -

Ukraine's President Volodymyr Zelensky criticises a decision by UN Secretary General Antonio Guterres to visit Moscow on Tuesday, instead of travelling first to Kyiv.

Guterres will meet Zelensky on Thursday, but the Ukrainian leader argues there is "no justice and no logic" in his visiting Russia first.

- Blinken to visit Ukraine -

US Secretary of State Antony Blinken will visit Kyiv Sunday, the day the Russian invasion of Ukraine enters its third month, says Zelensky.

US Defense Secretary Lloyd Austin will also visit, he adds. A US State Department official declines comment.

- Russia says hit arms depot -

Russia's defence ministry announces a missile strike on a depot containing weapons delivered by the United States and European countries to Ukrainian forces near Odessa.

It was among 22 Ukrainian military sites Russia targetted by missiles Saturday, while Russian warplanes attacked 79 military sites, the ministry adds.

- Poland major arms delivery -

Poland has supplied Ukraine with weapons to the value of $1.6 billion, says Prime Minister Mateusz Morawiecki.

Reports in the Polish media say the package includes 40 tanks and around 60 armoured cars.

- Nearly 5.2 million flee -

The number of Ukrainians fleeing the country since Russia's invasion is now 5,163,686, the UN refugee agency says.