Police shot at anti-government protesters in the Yemeni cities of Taiz and Hudaida, which the U.S. State Department called an "appalling" escalation of violence Monday. President Ali Abdullah Saleh -- a key U.S. ally against al Qaeda in Yemen, has been under increasing pressure from activists and protesters to leave office. Violence has increased in the country since Saleh's offer to leave after elections in the fall was rejected. The defection of key generals to the side of protesters has further undermined his grip on power.

In Taiz, south of the capital, Sanaa, police reportedly shot at protesters trying to storm the provincial government building, killing at least 15 and wounding 30, hospital sources told Reuters news service.

Police and armed men in civilian clothes fired bullets and tear gas at hundreds of demonstrators marching on a presidential palace in the Red Sea port city of Hudaida, officials in Yemen said.

A State Department spokesman said the United States was talking to the government in Yemen and to opposition leaders in hopes of achieving "a peaceful solution."