The U.S. is postponing a ballistic missile test that was previously scheduled for this week, the Pentagon announced Wednesday.

The decision is intended to defuse tensions and demonstrate that the U.S. is a responsible nuclear power, in contrast to Russian President Vladimir Putin, who put his nuclear forces on high alert Sunday.

The Pentagon called Putin’s decision a dangerous and irresponsible step.

As the battle in Ukraine rolls on, weapons from the United States are continuing to make their way into the country, officials confirmed.

After multiple days of heavy fighting, Ukrainian forces are holding on. The Pentagon believes a Russian convoy that’s nearly 40 miles long has been stalled.

A senior defense official told NewsNation they don’t know if it was bad planning or bad execution that’s led to the convoy’s slowdown — adding that Russian forces have had morale problems.

The senior defense official provided multiple reasons for the convoy’s hold up, including:

1: Ukrainian President Zelenskyy still in control of his army

2. Ukraine receiving weapons and support from the U.S. and other countries

3. Ukraine making good use of their assets

4. Ukrainians having the will to fight

Pentagon spokesperson John Kirby provided an update on Ukraine’s fight to hold off Russian forces Wednesday.

“They have not taken any of the major population centers that they appear to be wanting to take. And again, we think that there’s a variety of reasons for that and not least of which is the bravery and the skill and the creativity of Ukrainian fighters,” Kirby said.

Russia’s advance has been slower than expected but the Pentagon notes that troops are still moving forward, still focused on moving into the capital, and still intent on taking over the government.

Russian forces have a significant amount of combat power they have not yet engaged in the fight.