Russia-Ukraine updates: US sanctions Russian military shipbuilder, diamond miner

About 500 Ukrainian refugees were camped out Thursday outside the port of entry in Tijuana, Mexico, waiting to get into the United States after taking a circuitous route out of their war-torn country more than 10,000 miles away.

The number of Ukrainian refugees at the U.S. southern border entry point grew overnight from about 200 on Wednesday.

Immigration attorneys and humanitarian groups told ABC News that more and more Ukrainians have been showing up at the U.S. border this week, many of them getting there by flying to Mexico City, Mexico, and either taking a connecting flight to Tijuana or driving there.

Among the campers are also many Russians who oppose Russian President Vladimir Putin's decision to invade Ukraine, some telling ABC News they believe they would have been killed had they stayed in their homeland.

Ukrainians have asked for asylum in the United States and in many cases, have been allowed into the country under an exemption to Title 42, the federal policy that halted asylum claims during the pandemic. Some of the refugees allowed in the United States are being housed in San Diego, while others have spread out across the country.

Humanitarian groups are questioning the handling of the Ukrainians and Russians at the border versus all the other migrant groups fleeing horrific situations, including those coming from Haiti and Central America.

-ABC News' Will Carr

Russian troops are giving back control of the Chernobyl nuclear power plant to Ukraine, according to a letter from Russia's nuclear power company, Rosatom.

The site had been under the control of Russian forces since the invasion began on Feb. 24.

The letter is dated March 31 and was signed by Ukraine's nuclear regulator, Energoatom.

-ABC News' Fidel Pavlenko

Russian President Vladimir Putin has signed a decree requiring payment in rubles for gas exports.

As of Friday, Putin said all buyers from "unfriendly" countries -- including Germany, France and Poland -- must open ruble accounts in Russian banks, and contracts with parties who refuse will be deemed null and void.

President Joe Biden will be releasing one million barrels of oil per day from the strategic petroleum reserve for the next six months, according to the White House.

"Because of Putin’s war of choice, less oil is getting to market, and the reduction in supply is raising prices at the pump for Americans. President Biden is committed to doing everything in his power to help American families who are paying more out of pocket," the White House said in a statement Thursday.

A warehouse belonging to the International Committee of the Red Cross (ICRC) was shelled in Ukraine's besieged port city of Mariupol.

A satellite image shows the damage to the building, which bears a large white sign with a red cross on the roof.

"We can confirm that an image being circulated online shows damage to the ICRC warehouse in Mariupol," the ICRC said in a statement Wednesday. "We do not have a team on the ground there, so have no other information on potential casualties or the extent of the damage."

The Geneva-based humanitarian organization said it had distributed all supplies from the Mariupol warehouse earlier in March, including medical supplies to hospitals and relief supplies to people living in shelters. No ICRC staff have been at the warehouse since March 15 and it was unclear how the building has been used since, according to the organization.

The ICRC noted the "massive humanitarian needs" in Mariupol, but said it has been "unable to bring in more supplies due to the intensity of the fighting and the absence of a functional agreement between the parties to allow for the safe passage of humanitarian assistance."

"Under international humanitarian law, objects used for humanitarian relief operations must be respected and protected at all times," the ICRC said. "We are concerned that even a building with a red cross on it can be seriously damaged. Civilian infrastructure, hospitals and medical personnel cannot be targeted."

"But what we are most outraged by is the overall humanitarian situation in Mariupol and the relentless suffering inflicted on civilians living there," the organization added. "People are trapped with no safe way out of the city, and they are running out of the very basics needed for their survival. This must change."