Forces loyal to Yemen's President Ali Abdullah Saleh have opened fire on anti-government protesters in the capital, Sana'a, and the southern city of Taiz, killing at least five people.

Reports from Sana'a say that snipers on rooftops shot at marching protesters trying to enter a street that divides areas controlled by government forces from those held by dissident army units and a powerful tribal leader. Hospital workers say the shooting killed four people and wounded at least 35.

Activists say the demonstration Sunday drew tens of thousands of people calling for the president's resignation.

Security forces also shot at protesters in the southern city of Taiz, killing one woman.

On Saturday, violence in Sana'a claimed the lives of at least 18 people during another huge protest demanding the resignation of President Saleh.

Witnesses said security forces fired on protesters in the city center, killing at least 12 people, while the others were killed elsewhere in the capital as security forces battled supporters of opposition tribal leaders and dissenting soldiers.

Deputy Information Minister Abdou Janadi said the casualties were "unfortunate." He accused the opposition of provoking the clashes and using the protesters as a human shield.