Russia-Ukraine updates: Putin says 'certain positive movements' in negotiations

The Pentagon announced it will postpone an intercontinental ballistic missile test previously scheduled for this weekend to demonstrate that the U.S. is a "responsible nuclear power."

Pentagon press secretary John Kirby called out Russia for elevating its nuclear alert status and said the U.S. did not take its decision lightly. 

“Such provocative rhetoric and possible changes to nuclear posture involving the most consequential weapons and our respective arsenals is unacceptable,” said Kirby. “The United States has not taken any similar steps.”

“In an effort to demonstrate we have no intention in engaging in any actions that can be misunderstood, or misconstrued, the Secretary of Defense has directed that our Minuteman-III intercontinental ballistic missile test launch scheduled for this week to be postponed,” said Kirby. 

Kirby said that “in this time of heightened tensions” the U.S. and the international community saw Russia’s announcement as “dangerous and irresponsible and, as I've said before, an unnecessary step.”

Kirby said the decision to cancel the test is not a step back in U.S. readiness, and does not imply it will cancel other routine activities to ensure "credible nuclear capability."

-ABC News' Luis Martinez

The 40-mile-long Russian convoy has "stalled" and is not moving at a rate indicating they have solved their problems, a senior U.S. defense official said. 

The official said Wednesday they do not have perfect visibility into what's happening on the ground, but they believe the stall is due to several factors, one of which is stiff Ukrainian resistance north of Kyiv to include attempts to attack the convoy. 

"We have some indications that they have also at places and at times tried to target this convoy," the official said of the Ukrainian forces. 

Another factor continues to be "significant logistical and sustainment challenges."

"As for the food and fuel ... our assessment is that they are suffering shortages of both," the official said. 

As in days past, the official emphasized that "We would expect that the Russians will ... learn from these missteps and the stumbles and will try to overcome them."

"We think there's some degree that the purpose of this convoy is to help with resupply as well. So ... I think they're going to try to alleviate the food and fuel shortages that they've experienced," the official said.

About 82% of the Russian forces that were arrayed at the border are now inside Ukraine -- up from approx 80% yesterday, according to the official. 

Russia has now fired about more than 450 missiles against Ukraine since the beginning of the invasion, the official said. 

The official said that it is not always clear when civilians are being deliberately targeted by Russian attacks or are just being hit by errant strikes meant for nearby military targets. 

Airspace over Ukraine remains "very contested," the official said. 

Russians continue to fare better in the south. "They have been achieving more progress down there," the official said.

- ABC News' Matt Seyler

U.S. Secretary of State Antony Blinken announced that he will be traveling to Brussels, Poland, Moldova and the Baltic countries starting Thursday. 

Blinken will be continuing discussions and consultations with NATO allies and partners regarding the invasion of Ukraine, including consequences and severe economic costs on Russia.

In Brussels, he will participate in NATO and G7 summits and meet with EU counterparts, as well as hold additional meetings. 

In Poland, he will meet his Polish counterpart and "thank Poland for generously welcoming hundreds of thousands of displaced persons from Ukraine."

In Moldova, where Russian troops occupy the breakaway region Transnistria, Blinken will meet with leadership. 

Blinken will also be traveling to Estonia, Latvia and Lithuania, where he will reassure the three NATO allies about possible further Russian action. 

- ABC News' Conor Finnegan

At least some of the losses the Russians acknowledged Wednesday were due to weapons the U.S. provided Ukraine, acting U.S. Ambassador to Ukraine Kristina Kvien told ABC News.

The U.S. has supplied defensive weapons to Ukrainians including anti-tank Javelins and anti-aircraft Stingers, along with ammunition and other supplies.

"We don't know which individual piece of hardware did which individual thing, but let's just say my understanding is Javelins have been extremely effective against Russian onslaught," Kvien said.

"When you see on television some of these Russian tanks or planes blowing up that's partly due to the weapons we have been able to provide," she added.

Kvien told ABC News the U.S. would continue to push weapons and ammunition into the hands of the Ukrainians, but declined to discuss how they are getting into the country. 

-ABC News' Aaron Katersky