Pentagon: More Russian troops on Ukraine border

Russian combat troops are again building up along the border with Ukraine, and U.S. officials believe Moscow may be sending heavy weapons into the country to aid the separatists, the Pentagon said Wednesday.

Army Col. Steve Warren told reporters the U.S. believes there are now up to 12,000 Russia troops on the border, reflecting a steady increase in recent weeks.

On June 30, Air Force Gen. Philip Breedlove, the U.S. commander of NATO forces in Europe, said there were about seven battalion task groups and some small special operations forces along the border -- which officials said amounted to about 8,000 troops. The growing number of troops, he said, is "not a helpful development in what it brings to the problem."

The number has fluctuated widely. U.S. officials in May estimated that there were as many as 40,000 Russian troops arrayed along the border but as weeks went by, the total plunged to about 1,000 under pressure from the West.

Warren says there are a variety of Russian forces there, including the combat battalion task groups.

Ukraine and the West have accused Russia of fomenting the insurgency by sending troops and weapons, including tanks and rocket launchers, something Moscow denies.