Yemen president Ali Abdullah Saleh has ordered a state of emergency after regime loyalists killed at least 42 protesters in the deadliest incident in weeks of unrest.

Witnesses said pro-Saleh "thugs" rained bullets from rooftops around a square at Sanaa University, the centre of demonstrations against Saleh, adding that more than 300 people were wounded, according to a report in our sister publication, the Gulf Daily News.

Reports said protesters rushed into the surrounding buildings and threw six alleged gunmen from the rooftops.

"We were protesting peacefully and they shot at us. I won't leave this place until the president goes, even if I have to die," said one demonstrator, Ahmad, 25.

US President Barack Obama strongly condemned the violence, calling on his key anti-terror ally to live up to a pledge to allow peaceful protests and engage with the opposition.

The bloodshed brought the death toll to more than 70 since the outbreak of demonstrations calling for Saleh to step down after 32 years in power in late January.

"Most of the injured were shot in the head, neck and chest," a doctor said.

Many of the casualties were taken to a makeshift hospital at the university, where witnesses described bodies lined up with Qurans placed on their chests.

Saleh expressed his "regret" at the bloodshed, describing the victims as "martyrs of democracy" and accusing those responsible of trying to undermine a peace initiative backed by Saudi Arabia.

Saleh denied that police had fired any shots, while Interior Minister Mutahar Al Masri said they had intervened only after protesters "made several attempts to break into houses because they were trying to expand in the neighbourhood".

Yemeni parliamentary opposition spokesman Mohammed Al Sabri accused the regime of a "massacre" and said "these killings will not help keep Saleh in power". – TradeArabia News Service