Pro-Russian separatists likely used weapons supplied by Moscow to shoot down Ukrainian aircraft in recent weeks, NATO's top commander General Philip Breedlove said Monday. Russia was maintaining a large troop presence near Ukraine's border and had provided anti-aircraft weapons and other hardware to the rebels, Breedlove told a Pentagon news conference. Asked if the separatists used the weapons to take out Ukrainian aircraft in recent weeks, Breedlove said all the facts need to be "sorted out" but "I would say it's a very good likelihood" that Russian-supplied arms were behind the attacks. "What we see in training on the east side of the (Ukrainian) border, is big equipment, APCs (armored personnel carriers), anti-aircraft capability . . .and now we see those capabilities being used on the west side of the border," the general said. A Ukrainian military cargo plane was shot down on June 14, killing 49 people on board, and a Ukrainian helicopter was downed last week, leaving nine troops dead. Officials in Kiev blamed pro-Russian separatists for both incidents. Breedlove said the Russian military had more than seven battalion-sized task groups and "numerous" special operations forces deployed near the border. "That's not a helpful development," he said. Although there had been encouraging words from all sides promoting a truce, there was "continued conflict" on the ground and "continued support" for conflict from the Russian side of the border, he said. NATO would have to watch the situation "with a wary eye," he said. Breedlove, the supreme allied commander of NATO, said the crisis illustrated the need to avoid any further cuts to US forces in Europe. While there was room to scale back some unnecessary bases or other infrastructure for budget savings, Breedlove said he opposed any cuts to the number of troops stationed in Europe. "As far as force structure, I don't think we can take any more reductions," he said. Some additional US forces might be needed to deploy to Europe for temporary "rotational" missions, he said, as the transatlantic alliance seeks to bolster its profile in Eastern Europe and reassure allies due to tensions with Russia. The United States has roughly 66,000 troops in Europe, down from a peak of about 400,000 during the Cold War.