Yemeni troops opened fire Sunday on a large group of anti-government protesters in the capital, Sana'a, wounding at least 17 people with reports of at least one protester killed.

The shootings came hours before Yemeni President Ali Abdullah Saleh was expected to make a speech on state television. Mr. Saleh unexpectedly returned to the country Friday after a 3-month stay in neighboring Saudi Arabia while recuperating from a June assassination attempt.

Witnesses say the protesters Sunday were marching near the army's headquarters when troops opened fire.

Hundreds of other protesters demonstrated in Sana'a's Change Square, which has served as a center of anti-regime protests in the capital. Demonstrators prayed for protesters killed during the past week, one of the bloodiest since protests began in January.

On Saturday, clashes in Sana'a between forces loyal to the president and student protesters backed by dissident military units left at least 40 people dead. Government forces also attacked a student protest camp, causing many casualties.

A spokesman for opposition General Ali Mohsen al-Ahmar said at least 11 soldiers loyal to him were killed when their position came under fire.

Forces loyal to President Saleh reportedly have targeted the homes of tribal leader Sheikh Sadek al-Ahmar and his supporters, who no longer back Mr. Saleh.

The U.S. State Department has expressed deep concern about the situation in Yemen. A statement Saturday urged all parties to cease violence and exercise maximum restraint. It called on President Saleh to initiate a full transfer of power and arrange for presidential elections to be held before the end of the year.