General Breedlove sends 1200 NATO troops into Ukraine for exercises | 15 Sept. 2014 |

At the Wales meeting, NATO Secretary General Anders Fogh Rasmussen said a multi-national force of several thousand troops with a headquarters in Eastern Europe would shore up the 28-member alliance's commitment to NATO's Article V on collective defense.

Breedlove's briefing came as 200 paratroopers the 173rd Airborne Brigade arrived in Ukraine to join about 1,000 allied troops in the Rapid Trident joint training exercises with Ukrainian forces through Sept. 26, the Pentagon said.

Paratroopers of the 173rd Airborne Brigade of the U.S. Army in Europe take part in military exercise "Black Arrow" in Rukla, Lithuania, on May 14, 2014.

In April, the 173rd Sky Soldiers also took part in an unscheduled training exercise in Poland.

In a statement, Russia's Foreign Ministry has denounced the U.S. troop presence in Ukraine.

"They risk wrecking the progress made in the peace process in Ukraine, and encourage a deepening of the split in Ukrainian society."

Gen. Philip Breedlove, the NATO commander, said that Russia's hybrid warfare relied on "little green men" - Russian troops without insignia - to stir unrest in Russian-speaking areas as Russia built up heavy forces on the borders to open up supply routes.