Yemeni troops loyal to President Ali Abdullah Saleh opened fire Sunday on anti-government protesters in the capital, Sana'a, killing at least two people.

Activists say an unknown number of protesters were wounded in the pro-democracy demonstration that had drawn a crowd of tens of thousands of protesters calling for the president's resignation.

Sunday's violence comes a day after security forces fired on a massive rally in Sana'a, killing at least 18 people and wounding dozens of others.

Witnesses said at least 12 of the deaths occurred when security forces opened fire on protesters in the city center, while the rest were killed elsewhere in the capital as security forces battled supporters of opposition tribal leaders and dissenting soldiers.

Saturday's march began at Sana'a University, where demonstrators shouted anti-government slogans and carried banners calling for President Saleh's resignation.

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.