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 . `` The Yemeni people will not stay quiet on the blood that was spilled in Aden and we will avenge for them , '' said Hussein Ahmar , president of the Yemen Solidarity Council , on Saturday . Witnesses say the victims are anti-government demonstrators .
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 .