At least 42 protestors have been killed and hundreds more injured at an anti-government rally in the Yemeni capital of Sanaa.
Unidentified gunmen on rooftops opened fire on crowds after Friday prayers.
Yemen President Ali Abdullah Saleh declared a national state of emergency but denied his forces were behind the shooting.
Mr Saleh, who is struggling to maintain his 32-year grip on power in the Arab state, said the deaths had occurred in clashes between demonstrators and other citizens at a protest encampment at Sanaa University.
‘I express my extreme sorrow for what happened today after Friday prayers in the university district,’ Mr Saleh told a news conference in Sanaa.
‘The police were not present and did not open fire,’ he said. ‘It is clear there are armed elements inside these tents and they are the ones who opened fire.’
He declared a 30-day state of emergency that gives wider powers to security forces and bars citizens from bearing arms in public. A curfew was being discussed.
Yemen, home to an active al-Qaeda wing, is the second country in the region to announce emergency rule this week, after Bahrain's introduction of martial law on Tuesday, which was followed by a major crackdown on protesters.
