A rescuer is seen next to a residential building damaged by shelling, amid the Russian invasion of Ukraine, in Mykolaiv, Ukraine, in this handout picture released March 8, 2022.  Press service of the State Emergency Service of Ukraine/Handout via REUTERS
A rescuer is seen next to a residential building damaged by shelling, amid the Russian invasion of Ukraine, in Mykolaiv, Ukraine, in this handout picture released March 8, 2022. Press service of the State Emergency Service of Ukraine/Handout via REUTERS Reuters / STATE EMERGENCY SERVICE

The Ukrainian government on Tuesday accused Russian forces of shelling a humanitarian corridor that Moscow had promised to open to let residents flee the besieged port of Mariupol as the civilian death toll in the conflict mounted.

U.S. President Joe Biden was expected to announce a ban on Russian oil later on Tuesday, a significant step in Western powers' response to the Russian invasion.

With the war in its 13th day, the number of refugees who have fled Ukraine to neighbouring countries has surged past 2 million in what the United Nations describes as one of the fastest exoduses in modern times.

In Mariupol, hundreds of thousands of people have been sheltering under bombardment without water or power for more than a week.

"Ceasefire violated! Russian forces are now shelling the humanitarian corridor from Zaporizhzhia to Mariupol," Ukraine's foreign ministry spokesperson Oleg Nikolenko wrote on Twitter.

Ukraine's President Volodymyr Zelenskiy said a child had died of dehydration in Mariupol because water was cut off. The claim could not be independently verified.

Russia opened a separate corridor allowing residents out of the eastern city of Sumy on Tuesday, the first successful evacuation under such a safe route.

Buses left Sumy for Poltava further West, only hours after a Russian air strike which regional officials said had hit a residential area and killed 21 people. Russia denies targeting civilians.

The Russian defence ministry said 723 people had been evacuated through the Sumy-Poltava corridor, including 576 Indian nationals, in a first convoy.

Residents were also leaving the town of Irpin, a frontline Kyiv suburb. Residents ran with children in strollers or cradling babies in arms, while others carried pets and plastic bags of belongings.

"The city is almost ruined, and the district where I'm living, it's like there are no houses which were not bombed," said one young mother on Monday, holding a baby beneath a blanket while her daughter stood by her side.

The United Nations human rights office said it had verified 1,335 civilian casualties in Ukraine, including 474 killed and 861 injured, since the invasion kicked off on Feb. 24. But the true toll was likely to be higher, it said.

There were allegations of hundreds of civilian casualties in Volnovakha, Mariupol and other urban areas from bombing and shelling of residential areas, it said.

Moscow denies targetting civilians. It describes its actions as a "special operation" to disarm Ukraine and unseat leaders it calls neo-Nazis. Ukraine and its Western allies call this a baseless pretext to invade a country of 44 million people.

OIL SANCTIONS

Western sanctions have already cut off Russia from international trade and financial markets. Two people familiar with the matter told Reuters that Biden would announce a ban on Russian oil on Tuesday.

Russia is the world's biggest exporter of oil and natural gas, and until now its energy exports had been exempted from the international sanctions.

Although the United States is not a leading buyer of Russian oil, its allies are likely to come under pressure to also wean their economies off Russian energy.

The U.S. announcement will also intensify the impact of the war on a global economy already suffering supply shortages and price surges as it lurches out of the pandemic crisis. In the United States, gas pump prices have already hit a record since Russia launched the invasion.

"That's the cost of standing up for freedom and standing alongside the Ukrainian people, but it's going to cost us," U.S. Senator Chris Coons, a Democrat, told CNN.

Britain's Shell, one of several Western oil majors to announce it is pulling out of Russian projects, went further on Tuesday, saying it would no longer buy any Russian oil or gas and apologising for buying a Russian crude shipment last week.

The war could also worsen global shortages of other commodities since both Russia and Ukraine are major exporters of food and metals. Trade in London of the industrial metal Nickel was suspended on Tuesday after prices doubled within hours.

CORRIDORS

Corridors to let civilians escape and allow aid reach besieged areas have been the main subject of talks between Russian and Ukrainian delegations.

Russia's Interfax news agency said Moscow was opening humanitarian corridors for the cities of Sumy, Mariupol, Cherhihiv, Kharkiv and the capital Kyiv.

Ukraine has rejected Russian proposals for Kharkiv and Kyiv that would lead evacuees to Russia or its ally Belarus. Earlier attempts at the weekend to evacuate residents from Mariupol failed, with each side accusing the other of continuing to fire.

Moscow said Ukrainian authorities had endorsed only one civilian evacuation route out of 10 proposed, Interfax reported.

Western countries say Russia's initial battle plan for a rapid strike to topple the Kyiv government failed in the early days of the war, and Moscow has adjusted tactics for longer sieges of cities.

"The tempo of the enemy's advance has slowed considerably, and in certain directions where they were advancing it has practically stopped," Ukrainian presidential adviser Oleksiy Arestovych told a televised briefing on Tuesday.

Ukraine's defence ministry said Vitaly Gerasimov, first deputy commander of Russia's 41st army, was killed on Monday, the second Russian major general killed since the invasion began. Russia's defence ministry could not be reached for comment.

The main Russian assault force heading towards Kyiv has been stuck on a road north of the capital. But to the south, Russia has made more progress along the Black and Azov Sea coasts.

Within Russia, the war has led to a severe new crackdown on dissent, with the last remaining independent media largely shut last week and foreign broadcasters banned.

Russian police arrested at least 100 protesters against the invasion of Ukraine on Tuesday, the OVD-Info monitoring group said. There was no immediate comment from the police.

The top U.N. human rights official, Michelle Bachelet, said earlier that 12,700 people in Russia had already been detained at anti-war demonstrations.