The majority of military capability the U.S. promised to send Ukraine, part of a $350 million package, will be delivered within the next week, a senior U.S. defense official told reporters Friday.

In addition to the U.S., 14 countries are also providing military assistance to Ukraine.

The new aid package was expedited so quickly because it has been categorized as “a presidential drawdown,” which bypasses the traditional process of congressional notification, according to the official.

According to another official, this is the largest-ever military support that falls under “a presidential drawdown."

A second official told reporters that weapons were getting into Ukraine through "multiple venues."

Instead of providing new weapons, the U.S. will provide weapons that are in the existing U.S. military arsenal and are eligible to be replaced. The official said the Ukrainians are being provided with weapons they have already received training for in the past.

"I think all of us have been tremendously impressed by how effectively the Ukrainian Armed Forces have been using the equipment that we've provided them," said the official.

Adding, "I think that Kremlin watchers have also been surprised by this, and how they have slowed the Russian advance and performed extremely well on the battlefield."

-ABC News' Luis Martinez

U.S. envoy Linda Thomas-Greenfield addressed the Security Council Friday, warning that, "the world narrowly averted a nuclear catastrophe last night. We all waited to exhale as we watched the horrific situation unfold in real time."

She called Russia's attack on the Zaporizhzhia nuclear power plant "incredibly reckless and dangerous" and said it "threatened the safety of civilians across Russia, Ukraine and Europe."

Thomas-Greenfield urged Russia to withdraw troops from the facility, give operators full access to ensure continued safe operation and assess any damage and to halt any further use of force near Ukraine's nuclear facilities.

She said Russia has killed "thousands of Ukrainians" and "thousands" of Russian soldiers have been killed as well, adding, "President Putin must stop this humanitarian catastrophe by ending this war."

She called on Russia's envoy in the chamber to "say this won't happen again."

International Atomic Energy Agency Director General Rafael Grossi attended the meeting remotely, saying the agency was ready to deploy to Ukraine and establish "basic principles of safety and security starting with the physical integrity" of its nuclear power plants.

Ukraine has requested direct assistance, he said, calling it his agency's "duty" to assist.

The IAEA remains in contact with Ukrainian authorities, including Ukraine's nuclear regulatory agency and the company operating the facility, he said.

-ABC News' Conor Finnegan

Russia's state censor announced Friday it is blocking Facebook in the country.

The state censor, Roskomnadzor, claimed it was taking the step because of alleged freedom of speech violations by Facebook, citing the blocking of several Russian state media channels from the social media platform.

This is part of a broader push by Russian authorities to shut down independent media and social media platforms that might spread dissent against the war in Ukraine.

On Friday, the BBC announced it is temporarily pausing reporting from Russia because of a new law that imposes 15 years in jail for anyone spreading information the authorities claim is “fake” about the war in Ukraine.

-ABC News' Patrick Reevell

Approximately 100,000 children in Ukraine were raised in institutions prior to the war, according to government statistics, a United Nations Children's Fund spokesperson told ABC News.

The spokesperson said many of these institutions are located in hot spots.

These institutions are being evacuated without proper monitoring of the children's situation, according to UNICEF.

The spokesperson said many of the children in institutions like boarding schools and orphanages have disabilities.

- ABC News' Zoe Magee

The Russian forces charging toward Kyiv haven't made progress in the last day as they face Ukrainian resistance and low food and gas supply, a senior U.S. defense official told reporters Tuesday.

However, it could be a deliberate pause, the official said. "Part of the stall could be ... as a result of their own self-determined sort of pause in operations -- that they are possibly regrouping, rethinking, reevaluating," the official said.

The U.S. believes Russian forces "have committed now more than 80% of what was their pre-staged combat power," the official added.

The official said some Russian soldiers weren't told they were going into combat. The official said "not all of them were apparently fully trained and prepared."

The strong Ukrainian resistance has also hurt morale, according to the official.

Russia has now launched more than 400 missiles on Ukraine, the official said. The U.S. believes Russia has launchers that could be used for thermobaric weapons, but cannot confirm their use, the official said.

Russian forces are making the most progress in the south. Russians are attacking Kherson in south Ukraine, which "appears very much to be contested city at this point," the official said.

Russians are also approaching Mariupol in southeastern Ukraine, and while they haven't yet entered the city, "they are close enough now that they could attack Mariupol with long range fires," the official said.

Two towns on the path to Mariupol are believed to be occupied by the Russians, according to the official.

The U.S. believes the Russians hope to move north out of Mariupol up to the heavily-contested city of Kharkiv. The official said they believe Russian forces are trying to encircle Kharkiv.

The U.S. official noted that they've seen "certain risk-averse behavior by the Russian military" over the last week.

"Take the amphibious assault, for instance. They put those troops ashore a good 70 kilometers away from Mariupol because they knew Mariupol was going to be defended and they could put them ashore in an uncontested environment. And they still haven't reached Mariupol," the official said.

"They are not necessarily willing to take high risks with their own aircraft and their own pilots," the official said.

"And of course we're seeing that on the ground -- the fairly slow and steady progress that they have made, and you guys are seeing it for yourselves on the ground where ... units are surrendering, sometimes without a fight."

-ABC News' Matt Seyler