Ukraine's leader on Wednesday made an emotive appeal to US lawmakers for greater Western intervention against Russia, which insisted its invasion was going "successfully" despite the West rallying to Kyiv's aid with arms and sanctions.

In a landmark virtual address to Congress, President Volodymyr Zelensky invoked Pearl Harbor, the 9/11 attacks and Martin Luther King Jr as he showed lawmakers the aftermath of three weeks of Russian attacks.

Four large blasts were heard from the centre of Kyiv early Tuesday
Four large blasts were heard from the centre of Kyiv early Tuesday AFP / Genya SAVILOV

Ukrainian officials said 10 people had been killed while queuing for bread in the northern city of Chernigiv, and an unspecified number died in a Russian strike on civilians fleeing the besieged city of Mariupol.

The Mariupol mayor's office later said Russian forces had struck a theatre sheltering hundreds of civilians.

Dull booms echoed across the deserted streets of Ukraine's capital Kyiv, with only an occasional vehicle passing through sandbagged checkpoints, and very few permits granted to break its latest curfew.

The Kyiv mayor said after the bombings it was a 'difficult and dangerous moment'
The Kyiv mayor said after the bombings it was a 'difficult and dangerous moment' AFP / Aris Messinis

Kyiv has been emptied of around half of its 3.5 million people but Eduard Demenchuk, a private-security employee in his 50s, was among those who have stayed.

"It's worrying, of course. It's war after all. But we try to stay calm, we won't allow panic," he told AFP by telephone, after stocking up on groceries for the duration of the curfew.

Ukraine's capital has been transformed into a war zone, with apartment blocks badly damaged from Russian bombardments
Ukraine's capital has been transformed into a war zone, with apartment blocks badly damaged from Russian bombardments AFP / Aris Messinis

"To tell the truth, I wasn't planning to leave Kyiv anyway," Demenchuk added. "If need be, we will take arms and will stand to defend the city."

Russian rocket fire also hit a train station in Zaporizhzhia, used by refugees fleeing Mariupol, regional authorities said.

Some 20,000 residents have been allowed to leave Mariupol. But exhausted, shivering evacuees speak of harrowing escape journeys and rotting corpses littering the streets.

Deadly blasts hit Kyiv
Deadly blasts hit Kyiv AFP / Paz PIZARRO

Kyiv rejected Russian demands to impose neutrality on Ukraine, and Zelensky demanded the United States and its NATO allies impose a no-fly zone, so that "Russia would not be able to terrorize our free cities".

Switching to English, Zelensky addressed US President Joe Biden, saying: "I wish you to be the leader of the world. Being the leader of the world means to be the leader of peace."

The UN says nearly 1.4 million children have now fled Ukraine since the conflict began -- nearly one per second
The UN says nearly 1.4 million children have now fled Ukraine since the conflict began -- nearly one per second AFP / Louisa GOULIAMAKI

Biden later announced the United States' "unprecedented" latest package of new weapons aid to Ukraine added up to $1 billion and that the US would help Ukraine acquire "longer range" anti-aircraft weapons.

The UN says nearly 1.4 million children have now fled Ukraine since the conflict began -- nearly one per second
The UN says nearly 1.4 million children have now fled Ukraine since the conflict began -- nearly one per second AFP / Louisa GOULIAMAKI

Zelensky's speech received standing ovations from the members of Congress, much like his prior addresses to the UK and EU parliaments -- which were also rich in historical references.

Russian President Vladimir Putin, however, also reached back to history as he denounced the West's "pogroms" against Russia and its sanctions "blitzkrieg", which he said had failed.

Russia invasion of Ukraine
Russia invasion of Ukraine AFP / Cléa PÉCULIER

At a televised government meeting, Putin insisted the invasion was "developing successfully, in strict accordance with plans".

"And we will not allow Ukraine to serve as a springboard for aggressive actions against Russia," he added.

NATO will hold an emergency summit next week in Brussels with Biden attending -- but it has so far resisted Zelensky's pleas for direct involvement for fear of starting World War III.

Biden promised $1 billion in fresh arms aid to Ukraine
Biden promised $1 billion in fresh arms aid to Ukraine AFP / Nicholas Kamm

NATO chief Jens Stoltenberg said the alliance would put "substantially more forces" on its eastern flank, but was not planning to deploy forces to Ukraine.

Biden and other NATO leaders have instead been stepping up military support for Ukraine including anti-tank weapons that have helped to stall Russian forces north of Kyiv.

Kyiv was under curfew as the capital braced for an offensive from encircling Russian forces
Kyiv was under curfew as the capital braced for an offensive from encircling Russian forces AFP / FADEL SENNA

The new aid announced by Biden on Wednesday adds $800 million to the $200 million allocated over the weekend from an aid package approved last week by Congress.

Zelensky had earlier responded to news that hackers had targeted Ukrainian TV news and inserted a bogus message demanding Ukraine lay down its arms.

The hack was "the latest childish provocation" from Moscow, he said.

The chief prosecutor of the International Criminal Court was in Ukraine to investigate Russian atrocities, the president added.

"So the occupiers will be held responsible for all of the war crimes against Ukrainians."

Russia was meanwhile ordered to end its invasion by another tribunal, the International Court of Justice, which deals with disputes between UN countries.

Ukraine and Russia held another round of peace talks, after Zelensky conceded that NATO membership was not on the table, in an apparent concession to Moscow.

Kremlin spokesman Dmitry Peskov said a "compromise" outcome would centre on Ukraine becoming a neutral state comparable to Sweden and Austria.

But while the talks remained ongoing, Zelensky's office gave the idea short shrift.

"Ukraine is now in a direct state of war with Russia. Consequently, the model can only be 'Ukrainian' and only on legally verified security guarantees," Kyiv's negotiator Mikhailo Podolyak said.

After a symbolic journey to Kyiv by rail of the leaders of Poland, the Czech Republic and Slovenia, International Committee of the Red Cross president Peter Maurer embarked on a five-day visit.

He noted the "enormous suffering by the civilian population" in Ukraine and stressed it was "utterly important" for the ICRC's neutral humanitarian work to be recognised on the ground.

The conflict has already sent more than three million Ukrainians fleeing across the border.

Western sanctions against Putin's regime have also stepped up this week, pushing Russia to the brink of default on its foreign debts.

Moscow was due Wednesday to pay $117 million on two dollar-denominated bonds -- the first interest payment that has fallen due since it was largely shut out of the Western financial system.

The Kremlin has sought to shut down domestic opposition to the war, blocking access to at least 15 Russian and foreign-based media including the BBC and investigation website Bellingcat.

Isolated internationally, Putin has turned to Chechnya and Syria to replenish his invasion force -- and to China for economic support.

Russian Patriarch Kirill -- who has supported Putin's war -- and Pope Francis meanwhile agreed in talks on the need for a "just peace", Kirill's office said.