Medical staff in Yemen say at least 20 people are now known to have been killed when forces loyal to President Ali Abdullah Saleh opened fire on anti-government demonstrators in the southern city of Taiz.
A doctor in the city says hundreds more people were wounded when soldiers reportedly moved in to end a four-month-old sit-in in the city.
The doctor told the BBC security forces shot at people in Freedom Square, where a large stage and tents were located, and later brought in bulldozers.
Taiz was one of the first cities in Yemen where demonstrators - inspired by popular uprisings in Tunisia and Egypt - chose to gather.
President Ali Abdullah Saleh refuses to step down despite months of protests and strong opposition from a key tribe.
Meanwhile, Yemen's air force has bombed suspected al-Qaeda fighters who have seized the southern town of Zinjibar, witnesses said.