SANAA: At least five people were killed when plainclothes gunmen opened fire on Yemeni protesters in the centre of the capital Sanaa on Thursday, witnesses and a hospital official said, a day after President Ali Abdullah Saleh signed a deal to hand over power.

Witnesses said the gunmen shot at protesters on Sanaa's Zubayr street. At least four bodies brought from the scene of the shooting were visible at a nearby hospital, where an official said the death toll so far was five.

Saleh signed an accord to surrender power after 33 years of autocratic rule and ten months of protests aimed at ending it. Thursday's violence underscored the obstacles in the way of a peaceful political transition.

"Government loyalists opened fire on a demonstration from rooftops, from inside shops and from a passing car," said Ibrahim Ali, a 22-year-old man at a local hospital, who had been wounded in the knee. As the shooting was happening, some witnesses said uniformed security forces took part.

Another protester said they had been denouncing any immunity from prosecution that Saleh would enjoy under the deal to turn over power to his deputy as a step toward early elections.

"We were marching on Zubayr street demanding Saleh and his followers be tried when were were attacked by armed men in civilian clothes who opened fire on us directly," the man, who identified himself as Nael, told Reuters.