NATO has activated its NATO Response Force, marking the first time the alliance has activated the potentially 40,000-person force for “a deterrence and defence" role, according to a NATO spokesperson. This means that the 8,500 American troops put on heightened alert in late January for this mission could soon be ordered to Europe.

The decision follows a meeting of NATO ministers Friday morning in Brussels.

To be activated, the 30 members of NATO must all agree to activate the force, which is under the command of Gen. Told Wolters, the Supreme Allied Commander of NATO.

-ABC News' Luis Martinez

Officials are seeing more signs that Russian President Vladimir Putin isn't interested in a diplomatic solution, a senior U.S. official said.

Russian troops are now resupplied and are planning multiple entrance points into Kyiv that will likely be carried out at once, the official said.

-ABC News' Martha Raddatz

After Russian forces seized the area around the Chernobyl nuclear power station, the facilities continue "to operate safely and securely," Ukraine's regulatory agency informed the International Atomic Energy Agency, the U.N. Nuclear watchdog said Friday.

There were slightly higher levels of radiation, but they are still "low and remain within the operational range measured in the Exclusion Zone since it was established, and therefore do not pose any danger to the public," the IAEA said.

One theory why the levels could have ticked up, according to the IAEA, is "heavy military vehicles stirring up soil still contaminated from the 1986 accident."

The Chernobyl power plant, the site of the world's worst nuclear accident, is located about 60 miles north of the Ukrainian capital, Kyiv. The Chernobyl exclusion zone begins almost immediately below Ukraine's border with Belarus.

The Russian Ministry of Defense said Friday that Russian troops took full control of the Chernobyl plant area on Thursday.

-ABC News' Conor Finnegan

A senior defense official confirms that there is a Russian "amphibious assault" underway along the Ukrainian coast from the Sea of Azov. The attack is to the west of Mariupol, which is a coastal city in southeastern Ukraine.

"Indications are right now that they are putting potentially thousands of naval infantry ashore there," the official said.

The push toward Kyiv is going slower than the Russians expected as they're meeting more resistance from Ukrainians than they thought, the official said.

“In general the Russians have lost a little bit of their momentum," the official said.

The official pointed out that no population centers have been taken and the Russians do not have air superiority over Ukraine as Ukrainian air defenses are still working.

The official said more than 200 ballistic and cruise missiles have been fired at targets in Ukraine, adding some have "impacted civilian residential areas."

The U.S. assesses that "a third of the combat power " of the 150,000 Russian troops that were amassed on border are actually dedicated to the fighting in Ukraine, according to the official. “They have not they have not committed the majority of their forces inside Ukraine," the official said.

Fighting is also underway at the Kakhovka hydroelectric power plant and dam on the Dnieper River that controls a lot of electrical power to Crimea and southern Ukraine, the official said, adding that there have been cyberattacks against power plants.

-ABC News' Matt Seyler, Luis Martinez