Russian missiles struck the site of a radioactive waste disposal facility in Kyiv overnight, Ukrianian officials told the International Atomic Energy Agency.

There were no reports of damage or any indications of a radioactive release, according to the IAEA.

The strike came a day after an electrical transformer at a similar disposal facility near the northeastern city of Kharkiv had been damaged. There were no reports of radioactive release at that facility.

“These two incidents highlight the very real risk that facilities with radioactive material will suffer damage during the conflict, with potentially severe consequences for human health and the environment,”  IAEA Director General Mariano Grossi said in a statement.

The disposal facilities typically hold disused radioactive sources and other low-level waste from hospitals and industry, according to the IAEA.

-ABC News' Christine Theodorou

In the first response to Russia raising the alert status of its strategic nuclear force, a senior U.S. defense official described the move as an "escalatory one."

The official pointed out that Russia has never been under threat by NATO or Ukraine and warned that Russia's heightened alert status is "clearly potentially putting at play forces that could if there's a miscalculation make things much, much more dangerous."

"We believe that this is not only an unnecessary step for him (Russian President Vladimir Putin) to take but an escalatory one," the official said. "Russia has never been under threat by NATO. Ukraine did not threaten Russia."

The official would not discuss the status of the U.S. nuclear force, saying "we do not talk about ... specifics of our strategic deterrent posture."

"I would just tell you that we remain confident in our ability to defend ourselves and our allies and our partners, and that includes in the strategic deterrent realm," the official said.

-ABC News' Luis Martinez

Ukraine has agreed to send a delegation to meet with Russian negotiators for talks at the border between Belarus and Ukraine, according to a spokesman for Ukraine’s president’s office.

President Volodymyr Zelenskyy agreed to the step during a phone call with Belarus’ authoritarian leader Alexander Lukashenko, the spokesman said.

The spokesman said the two sides have agreed to meet at the Pripyat river on the border, north of Chernobyl. That area is currently under Russian military control.

Russia earlier sent a delegation to the city of Gomel in southern Belarus to “be ready” for talks but Ukraine refused to hold them in Belarus since it is actively taking part in the invasion.

The Russian delegation includes officials from Russia’s foreign and defense ministries as well as the presidential administration.

-ABC News’ Patrick Reevell

Russian President Vladimir Putin has ordered his military to put Russia's strategic deterrence forces in a state of heightened readiness, saying it is a response to what he called "aggressive statements" from NATO countries.

In a televised meeting, Putin ordered his defense minister and chief of general staff to move Russia's forces, including the nuclear triad, into a "special regime of combat duty,"

The announcement appears to be intended as rattling Russia's nuclear saber at Western countries as they send large numbers of weapons to Ukraine and sanction Russia.

"Senior officials of the leading NATO countries allow aggressive statements against our country, therefore I order the minister of Defense and the chief of the General Staff to transfer the deterrence forces of the Russian army to a special combat duty regime," Putin said during a meeting with Defense Minister Sergei Shoigu and Chief of the General Staff of the Russian Armed Forces Valery Gerasimov.

-ABC News' Patrick Reevell and Tanya Stukalova

Secretary of State Antony Blinken closed his remarks to the U.N. Security Council meeting by challenging the Russian Federation to "announce today -- with no qualification of equivocation or deflection -- that Russia will not invade Ukraine, stated clearly stated plainly, to the world."

"And then demonstrate it by sending your troops, your tanks, your planes back to their various can hangars and sending your diplomats to the negotiating table," he added.

Blinken laid out how the U.S. believes Russia will attack Ukraine -- but said he would welcome being wrong and for Russia to withdraw.

"Now, I'm mindful that some have called into question our information, recalling previous instances where intelligence ultimately did not bear out," he said, apparently referring to a similar address then-Secretary of State Colin Powell famously made to the Security Council presenting U.S. intelligence to justify the Iraq War. "But let me be clear, I am here today not to start a war, but to prevent one," he said, citing allies that agree with U.S. assessments.

"If Russia doesn't invade Ukraine, then we will be relieved that Russia changed course and proved our predictions wrong. That would be a far better outcome in the course we're currently on. And we'll gladly accept any criticism that anyone directs at us," Blinken said.

He continued, "Russia can still make if there's any truth to his claim that is committed to diplomacy. Diplomacy is the only responsible way to resolve this crisis"

Blinken also said that he sent a letter to Russia's Foreign Minister Sergei Lavrov earlier Thursday proposing that they meet next week in Europe following their talks in recent weeks "to discuss the steps that we can take to resolve this crisis without conflict" and that U.S. is also proposing meetings at the NATO Russia Council and the OSC Permanent Council.

"These meetings can pave the way for a summit with key leaders in the context of de-escalation to reach understandings on our mutual security concerns," he added.