"We have new evidence that Russia is firing artillery to attack Ukrainian military positions," Xinhua quoted US State Department spokeswoman Marie Harf as saying on Thursday.
"We also have evidences to show that the Russians intend to deliver heavier and more powerful, multiple rocket launchers to the separatist forces in Ukraine," Harf said.
According to Harf, the evidences are based on intelligence information.
The US on Wednesday blamed Russian President Vladimir Putin for being responsible for the downing of Malaysian Airlines flight MH17 that killed 298 people on board.
US has also urged Moscow to ensure that the militants in eastern Ukraine allow free access to investigators and do not impede any probe.