NEW : Amnesty International says security forces are blocking access to hospital . The group said it had been told that the military was preventing ambulances from reaching a number of hospitals in the capital and surrounding areas. Yemini tribal leaders say they will join protests calling for the Saleh 's resignation . Witnesses say the victims are anti-government demonstrators .
NEW : Amnesty International says security forces are blocking access to hospital . Medical officials say four people died and 26 were injured after clashes in Aden . Yemini tribal leaders say they will join protests calling for the Saleh 's resignation . Witnesses say the victims are anti-government demonstrators .