Senior US intelligence officials told The Associated Press that Russia-backed rebels in the region were likely responsible, but they found no evidence of a direct link between Russia and the shootdown. The United States and Ukraine claim a Russian-built Buk anti-aircraft missile system was used in the attack on the plane; the Buk system is described as very sophisticated, and many analysts suspect the rebels would need supplies and training from Russian personnel to successfully shoot down a high-altitude plane like MH17.