Some Russian troops moved to firing positions near Ukraine, Putin said be ready by Feb. 16: Sources

It was still unclear whether the Russian president had decided to invade Ukraine, but President Joe Biden said there was no sign of a pullback.

While Russia's defense ministry said Tuesday that some forces would pull back from Ukraine's borders after completing military exercises, the U.S. has so far not seen that, President Joe Biden said in an address to the nation.

But worrying U.S. officials, Russians troops are instead moving forward closer to the line, including with medical supplies, and being put into firing positions, sources told ABC News.

The U.S. believes that Russia now has all the necessary pieces in place, including 150,000 troops in the region, to launch a swift and brutal invasion of Ukraine, the sources added -- the reason why Biden administration officials have now publicly been saying Russia could move "at any time."

In particular, ABC News has learned that Russian leader Vladimir Putin had told his military forces to be ready to go by Wednesday, Feb. 16, but it is still unclear whether he has made a decision to attack his neighbor.