The White House is expected to announce a ban on U.S. imports of Russian oil as soon as Tuesday, a source familiar with the matter told ABC News.

-ABC News' Cecilia Vega

Ukrainian President Volodymyr Zelenskyy said Tuesday that a child has died from dehydration in the besieged port city of Mariupol.

"Russia is for sure to blame for the deaths of people from airstrikes and in the blocked cities," Zelenskyy said in a televised address. "But the responsibility is also on those who during these 13 days can't make a decision in their offices in the West, an obviously necessary decision. Those who don't secure Ukrainian sky from Russian murderers, who didn't save our cities from airstrikes, these bombs and missiles, although they can."

"We have been hearing promises about support for 13 days that the jets are about to arrive," he added. "We have heard promises about securing humanitarian corridors. They didn't work. We don't have time to wait. People in Mariupol don't have time to wait."

Zelenskyy said trucks carrying humanitarian aid have been sent to Mariupol. He accused the International Committee of the Red Cross of "forbidding the use of its emblem on our cars," but did not give further details. Videos posted to social media on Tuesday purportedly show vehicles heading to Mariupol from other Ukrainian cities bearing signs with a red cross, but it's not clear who pasted them there.

"The drivers are heroes who understand they can be killed by Russian troops," Zelenskyy said. "If you kill those people, the whole world will be the witness."

-ABC News' Julia Drozd

Out of the more than 2 million people who have been forced to flee Ukraine since Russian forces invaded on Feb. 24, half of them are children, according to the United Nations International Children's Emergency Fund (UNICEF).

UNICEF spokesperson James Elder called it a "dark historical first."

Energy giant Shell announced Tuesday plans to withdraw from its involvement in all Russian hydrocarbons, including crude oil and natural gas, amid Russia's unprovoked invasion of neighboring Ukraine.

"As an immediate first step, the company will stop all spot purchases of Russian crude oil. It will also shut its service stations, aviation fuels and lubricants operations in Russia," Shell said in a statement.

Shell will immediately stop buying Russian crude oil on the spot market and not renew term contracts. The company will also change its crude oil supply chain to remove Russian volumes, but said "this could take weeks to complete and will lead to reduced throughput at some of our refineries."

In addition, Shell will shut its service stations, aviation fuels and lubricants operations in Russia, and will start a phased withdrawal from Russian petroleum products, pipeline gas and liquefied natural gas.

The company apologized for buying Russian oil last week.

"We are acutely aware that our decision last week to purchase a cargo of Russian crude oil to be refined into products like petrol and diesel -- despite being made with security of supplies at the forefront of our thinking -- was not the right one and we are sorry," Shell CEO Ben van Beurden said in a statement. "As we have already said, we will commit profits from the limited, remaining amounts of Russian oil we will process to a dedicated fund. We will work with aid partners and humanitarian agencies over the coming days and weeks to determine where the monies from this fund are best placed to alleviate the terrible consequences that this war is having on the people of Ukraine."

Ukrainian Foreign Minister Dmytro Kuleba took to Twitter to praise Shell "for taking this moral and responsible step," and he encouraged "other world businesses to follow suit."

U.S. Secretary of State Antony Blinken crossed the border into Ukraine Saturday after meeting with Ukrainian Foreign Minister Dmytro Kuleba at the Korczowa Border Crossing Point.

"The entire world stand with Ukraine," Blinken said, and Kuleba added that he hopes Ukrainians will see this as a "clear manifestation that we have friends who literally stand by us."

Blinken said the sanctions imposed so far against Russia are "producing very, very concrete results" and that the pressure will "grow" until this "war of choice is brought to an end."

When asked directly about helping Kuleba with more firepower, Blinken said, "the support for Ukraine not only has been unprecedented, not only is going to continue, it's going to increase."

Kuleba said Ukraine "appreciates" sanctions that have been announced in the last week, but that more economic and political pressure and "necessary weapons," would "save many lives in Ukraine... many sufferings will be avoided."

Kuleba also said that they are “satisfied" with already arranged supplies of anti-tank weapons and ammunition, but that “it’s no secret” they still want fighter jets and air defense systems.

He also thanked the U.S. for sending stingers, and said they were used on Saturday.

"Just today we shot down three Russian attack aircrafts, which were bombing our cities with the use of stingers but we need -- so to say -- big air defense systems to ensure the safety of our skies. If we lose the skies, there will be much, much more blood on the ground,"Kuleba said.

In response to questions about NATO’s refusal to impose a no-fly zone over Ukraine, Kuleba said it’s a "sign of weakness," but stayed optimistic that they will change their minds.

"The time will come," he said.

-ABC News' Conor Finnegan and Justin Gomez