Ukraine says five railway stations that are vital to ferrying supplies and refugees across the country have been hit by missile strikes as Russia attempts to block military equipment from other countries.

Russia’s defence ministry confirmed its missiles destroyed six substations powering the railways used to transport foreign weapons.

“Russian forces are systematically destroying the infrastructure of our railways,” wrote the head of Ukraine’s rail network, Olexandr Kamishin, of the attacks in the central and western regions.

It comes as the US pledged new assistance worth $US713 million ($984 million) to Ukraine and other countries in the region that are fearful of Russian aggression.

US Defence Secretary Lloyd Austin and Secretary of State Antony Blinken visited Ukraine’s capital Kyiv and hailed its success so far against Russia’s invasion.

“What you’ve done in repelling the Russians in the battle of Kyiv is extraordinary and inspiring quite frankly to the rest of the world,” Austin told President Volodymyr Zelensky.

“We are here to support you in any way possible.”

At a briefing in Poland, Mr Blinken said Russia “has already failed” in its war aims while “Ukraine has already succeeded”.

With the Russians out of the capital, Ukrainians can walk freely in Kyiv. Photo: Getty

Both men said on Monday the fact they could come to Kyiv was proof of Ukraine’s tenacity in forcing Moscow to abandon an assault on the capital last month.

Just weeks ago, Kyiv was a frontline city under curfew and bombardment, with tens of thousands of Russian troops massing on its northern outskirts. Residents spent nights huddled in its metro stations, sheltering from artillery.

Today, the nearest Russian troops are hundreds of miles away, normal life is returning to the capital, Western leaders have been visiting and countries are reopening their embassies.

The US has promised to reopen its embassy in Kyiv soon and Mr Blinken said American diplomats would first return to Lviv in the west and should be back in Kyiv within weeks.

Despite Ukraine having repelled the assault on Kyiv, the war is far from over.

Regular morning air raid sirens across Ukraine lasted more than two hours, much longer than usual.

Ukraine has reported more Russian offensives to take full control of the Donbas – the eastern Donetsk and Luhansk regions, partially held by Russian-backed separatists since 2014 – and to link them and Crimea, which Moscow annexed in that year.

Ukraine’s general staff said Russia was shelling its second biggest city, Kharkiv, in eastern Ukraine and towns and villages to the south but that Ukrainian forces had staved off assaults on three settlements.

‘Ceasefire’ in Mariupol

Russia has announced a new ceasefire and a humanitarian corridor for civilians trapped in a steel plant in the besieged Ukrainian port city of Mariupol.

According to the Defence Ministry in Moscow, the Russian army was set to cease hostilities at 2pm local time on Monday and civilians should then be able to leave the industrial zone via a humanitarian corridor.

The Azovstal steel plant became a last refuge for the people still trapped in Mariupol.

According to Russian sources, about 2500 Ukrainian fighters and foreign mercenaries are still there. Kiev says there are also 1000 civilians in the steel plant.

Early on Monday, a series of Russian offensives were blocked in eastern Ukraine, according to reports out of Kiev.

-with AAP