But those sanctions have so far failed to stem the flow of weapons or the fighting, which appeared to enter a dangerous new phase Tuesday on reports that Ukraine's government had used short-range ballistic missiles against the rebels, according to three U.S. officials.
The weapons have a range of about 50 miles (80 kilometers) and pack up to 1,000-pound (454-kilogram) warheads. If the reports are accurate, they are the most deadly missiles to date used in the conflict.
The officials did not specify exactly where the missiles hit or what damage they caused.
One U.S. official said so far, there has been no reaction from Russia. A second official said it is not clear if the United States will show satellite imagery of the Ukrainian firings "because these are the good guys."