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."

Russian troops "are not withdrawing" from parts of Ukraine as claimed, but rather are "repositioning," according to NATO Secretary-General Jens Stoltenberg, who cited NATO "intelligence."

"Russia has repeatedly lied about its intentions," Stoltenberg said at a press conference Thursday. "Russia is trying to regroup, resupply and reinforce its offensive in the Donbas region [in eastern Ukraine]."

Meanwhile, pressure is being maintained on Ukraine's capital, Kyiv, and other major cities, according to Stoltenberg.

"We can expect additional offensive actions bringing even more suffering," he added.

All Russian troops have left the Ukrainian cities of Kyiv and Chernihiv, withdrawing north toward the borders of Belarus and Russia to consolidate before likely redeploying to the Donbas region in eastern Ukraine, a senior U.S. defense official told reporters Wednesday.

But even with the Russians gone, the territory remains treacherous.

"There are some indications that they left behind mines and things like that, so the Ukrainians are being somewhat careful in some areas north of Kyiv as they begin to clear the ground and clear the territory and re-occupy it," the official said.

While the U.S. hasn't yet seen these troops redeploy elsewhere in Ukraine, it'll likely happen soon, according to the official. Ukrainian forces are preparing for a major fight in Donbas, the official said.

The official also said the Pentagon is "monitoring" an apparent nitric acid explosion in Ukraine's Luhansk region, which Russia blamed on Ukraine.

"We've seen the Russians claim that this was a Ukrainian attack on this. We do not believe that is true," the official said. "We do believe that the Russians are responsible, but exactly what they used when they did it, why they did it, what the damage is, we just don't have that level of detail," the official said.

The official also noted that a small number of Ukrainians currently in the U.S. for "professional military education" were pulled aside for a couple days of training on Switchblade drones, which the U.S. is sending overseas as part of its military aid, according to the official.

"Although it's not a very difficult system to operate, we took advantage of having them in the country to give them some rudimentary training on that," the official said.

-ABC News' Matt Seyler