'No reason' to change US nuclear alert level amid Putin's threat: Psaki

As the U.S. and other Western nations considered how to address Russian aggression, the Pentagon and White House said Monday the U.S. saw no need to change the its nuclear alert level despite Russian President Vladimir Putin making a a veiled threat Sunday that he was doing so, placing his forces on "special combat readiness."

"We are assessing Putin's directive and at this time we see no reason to change our own alert level," White House press secretary Jen Psaki said.

"The United States nor NATO has any desire for conflict with Russia, and we think provocative rhetoric like this regarding nuclear weapons is dangerous, adds to the risk of miscalculation, should be avoided, and we'll not indulge in it," she said.

Asked by a reporter after a Black History Month event whether Americans should be worried about nuclear was, President Joe Biden quickly responded, "No."

Psaki also said that the $350 million in aid that Biden approved to be delivered to Ukraine will arrive "within the next couple of days" although that has been complicated by disputed airspace over and near Ukraine. At the same time, she effectively ruled out NATO enforcing a no-fly zone in the area.

Earlier Monday, Biden held a call with allies and partners to coordinate the ongoing response to as Ukraine and Russia held talks on a possible cease-fire in the invasion.

The call included European Commission President Ursula von der Leyen, French President Emmanuel Macron, German Chancellor Olaf Scholz, Japanese Prime Minister Fumio Kishida, NATO Secretary General Jens Stoltenberg, Polish President Andrzej Duda, Romanian President Klaus Iohannis, and UK Prime Minister Boris Johnson.

That call comes as Russian and Ukrainian leaders met for talks for six hours at the Belarusian border on Monday morning.

A Ukrainian spokesman said in a statement afterward that there may be another round of negotiations.

"The Ukrainian and Russian delegations held the first round of talks today, the main purpose of which was to discuss the issues of a cease-fire on the territory of Ukraine and hostilities," Mikhail Podolyak said.

At the State Department, the U.S. response was skeptical.

"Diplomacy at the barrel of a gun, diplomacy at the turret of a tank – that is not real diplomacy," spokesperson Ned Price said. Though he said that the U.S., Ukraine, and European allies still believe dialogue is the way forward, he clarified that "diplomacy is highly unlikely to bear fruit – to prove effective – in the midst of not only confrontation, but escalation." Later, he said, "In order for it to bear fruit, it needed to take place in the context of de-escalation."

The White House on Monday also laid out more specifics about sanctions announced over the weekend in response to Russia's invasion of Ukraine.

The sanctions on Russia's Central Bank prevent the Russian government from access to more than $600 billion in reserves in the U.S., or in U.S. dollars in foreign countries. Officials said it was evident that Putin planned to use the central bank's assets to offset the effects of sanctions from Western countries.

A senior White House official said they "represent the most significant actions the U.S. Treasury has taken against an economy of this size, and assets of this size."

"Today's announcement that prohibit transactions with the Central Bank of Russia in the national wealth fund will significantly hinder their ability to do that, and inhibit their access to hundreds of billions of dollars in assets from our actions alone, they will not be able to access assets that are either in United States or in US dollars," officials said.

Beyond sanctions, the U.S., among other nations, is providing material support to Ukraine as it tries to beat back Russian forces. A senior defense official said Monday that the U.S. is continuing "to provide security assistance to Ukraine, and that includes in just the last day or so."

"We don't have any indications that that there's been a blockage or impediment to continued assistance coming from the west to the Ukrainian armed forces," the senior defense official said. "And as I said, that support continues to flow not just from the United States, but from other nations as well."

However, the defense official was hesitant to give specifics about the details of U.S. support to Ukrainian forces given so that the support is not "disrupted."

"I will remain reticent to talk about the methods in which and the ways in which we're going to look for ways to continue to provide our support precisely because we want to make sure it gets into the hands of Ukrainian armed forces and Ukrainian fighters and we don't want that to be disrupted," a senior defense official said.

Pentagon spokesman John Kirby declined to talk about the potential of that aid being disrupted during a press briefing Monday.

"We're going to continue to provide security assistance to Ukrainian armed forces, and we're still going to look for ways to do that, in the most effective, efficient way possible," Kirby said.

ABC News' Sarah Kolinovsky, Justin Gomez, Matt Seyler, Conor Finnegan, Benjamin Gittleson, Joseph Simoetti and Libby Cathey contributed to this report.