Syrian forces loyal to President Bashar al-Assad have fired Scud missiles at rebel fighters in recent days, Obama administration officials said on Wednesday.

The move represents a significant escalation in the fighting, which has already killed more than 40,000 civilians in a nearly two-year-old conflict that has threatened to destabilize the Middle East, and suggests increased desperation on the part of the Assad government. A fresh wave of mayhem struck the Syrian capital Damascus on Wednesday, reports from the region said, including a deadly triple bombing outside the Interior Ministry. One American official, who asked not to be identified because he was discussing classified information, said that missiles had been fired from the Damascus area at targets in northern Syria.