Kyiv Oblast's regional police chief said Friday that the number of civilians killed there has reached 900.

Two mass graves found in Bucha, a city in Kyiv Oblast, outside of the capital of Kyiv, added significantly to the toll, Kyiv Region Police Chief Andriy Nebytov said. Forty people were found in the first grave and 57 were found in the second. The vast majority of the victims had been shot.

"Bucha has the highest number of casualties, which means that the occupiers operating in Bucha were the most brutal. We have already taken more than 350 bodies from the city," Nebytov said.

A White House official on Friday confirmed that Russia has sent a formal diplomatic note to the United States saying weapons shipped to Ukraine from the U.S. and NATO were "adding fuel" to the conflict.

The note, reported by The Washington Post, said deliveries of the "most sensitive weapons" could result in "unpredictable consequences" for the U.S.

Biden on Wednesday authorized an additional $800 million in weapons for Ukraine.

NBC News has not seen the note, but a White House official who has confirmed the contents of the note reported by The Washington Post.

A State Department spokesperson said they would not confirm any private diplomatic correspondence.

But, the spokesperson said: "What we can confirm is that, along with Allies and partners, we are providing Ukraine with billions of dollars worth of security assistance, which our Ukrainian partners are using to extraordinary effect to defend their country against Russia’s unprovoked aggression and horrific acts of violence."

Seven people died when Russian servicemen fired on buses as they were evacuating civilians on Thursday, the office of Ukraine’s attorney general said in a statement posted to its Telegram channel. 

Another 27 people were injured in the incident which took place in Borova, a small village around 35 miles south of Kyiv, the statement, translated by NBC News, said. 

NBC News could not independently verify the claims and Russia has repeatedly denied it is targeting civilians.

Ukraine’s defense ministry spokesman Oleksandr Motuzyanyk said on Friday that for, the first time since the start of its invasion, Russia used long-range bombers to attack the besieged port city of Mariupol.

Motuzyanyk said Russia was concentrating its efforts on seizing the cities of Rubizhne, Popasna and Mariupol.

Hundreds of millions of people around the world “are going to be devastatingly impacted” by the war in Ukraine, David Beasley, the executive director of the World Food Programme, told NBC News by telephone Friday. 

“They produce enough food in Ukraine to feed 400 million people, so where is that food going to come from if Ukraine isn’t able to get it out of the fields, into the ports and then out of the ports,” Beasley said. “Right now that’s not happening so we’re going to have a global crisis unlike one we’ve never seen before.”  

He added that rising food and fuel prices were already having “a dramatic impact” on the WFP’s operational budget. 

“We buy 50 percent of our wheat from Ukraine, so you can imagine if we feed 125 million people throughout the year, it’s going to be devastating for our operations,” he said. 

Beasley said 45 million people were knocking on famine’s door in 38 countries, including Afghanistan, Ethiopia, Chad and Yemen. 

So if the Ukraine conflict did not end quickly it “will devastate global food security,” he said. 

“If the war doesn’t end in the next 30 days we’re talking about an extra 35 to 40 million people entering into extreme hunger,” he added.

Russian troops are digging up bodies previously buried in residential courtyards and not allowing new burials of “people killed by them,” the Mariupol City Council said Friday, citing reports from local residents.  

“In each yard they put their own overseer, who does not allow Mariupol residents to bury their deceased relatives or acquaintances,” the council said in the statement posted to its Telegram channel and translated by NBC News.  

“It is possible to assume that the Russian occupation forces are trying in every way to replace the traces of their war crimes in our city,” the statement added. 

NBC News could not independently verify these claims. 

Earlier this month, Mariupol Mayor Vadym Boychenko said that Russian forces had brought mobile cremation equipment to the city to dispose of the corpses of victims of the siege.

LVIV, Ukraine — Across the city here, Ukrainians are working collectively or individually to support the war effort.

Dmytro Zhultenko, who worked in software design and marketing, is operating one such effort from his home in Lviv. He keeps in contact with classmates who are now soldiers on the frontlines and organizes boxes of military supplies to support them.

While he sends a lot of tactical gear, he said the $150 he recently spent on chocolate to include in each package he ships out to his schoolmates would be “a game changer there for the morale.”

Zhultenko said he also bought about 10 cartons of cigarettes as an additional morale booster.

People are “starving to death” in the besieged city of Mariupol, according to David Beasley, the executive director for the United Nations World Food Programme.   

“Mariupol is the worst of the worst. We are not getting the access we need to reach the people, and when you go 50 days without food and any coming in, then you know people will be starving to death,” Beasley told NBC News by telephone Friday.  

“You can only imagine what is going on inside the city,” he said, adding that he had heard “horror stories” from people who managed to flee. 

Beasley said that he had written to Russian Foreign Minister Sergey Lavrov to say that the WFP needed access to Mariupol and several other cities in Ukraine.

“They need to let us in and feed the innocent victims of this war,” he added.