By Steve Holland and Pavel Polityuk
WASHINGTON/LVIV, Ukraine (Reuters) -U.S. President Joe Biden on Tuesday announced a ban on Russian oil and other energy imports, a significant move in stepping up the international pressure on President Vladimir Putin to halt his devastating assault on Ukraine.
"Russia may continue to grind out its advance at a horrible price, but this much is already clear: Ukraine will never be a victory for Putin. Putin may be able to take a city, but he'll never be able to hold the country," Biden told reporters at the White House.
On the ground in Ukraine, the Kyiv government accused Russian forces of shelling a humanitarian corridor that Moscow had promised to open to let residents flee the besieged port of Mariupol.
The civilian death toll in the conflict mounted. And with the war in its 13th day, the number of refugees who have fled Ukraine to neighbouring countries surged past 2 million.
Western sanctions imposed over the invasion have already cut off Russia from international trade and financial markets. 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.
"We're banning all imports of Russian oil and gas energy," Biden said. "That means Russian oil will no longer be acceptable in U.S. ports and the American people will deal another powerful blow to Putin's war machine."
The United States is not a leading buyer of Russian oil, but Biden has been working with allies in Europe, who are far more dependent on Russian oil, to isolate Russia's energy-heavy economy and Putin.
Britain announced shortly before Biden's remarks that it would phase out the import of Russian oil and oil products by the end of 2022.
In Mariupol, hundreds of thousands of people have been sheltering under bombardment without water or power for more than a week. Many tried to leave on Tuesday along a safe corridor but Ukraine said they came under Russian fire.
"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.
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.
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 targeting 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.
(Reporting by Reuters bureaus; Writing by Peter Graff and Angus MacSwan, Editing by Tomasz Janowski and Gareth Jones)