Sanaa , Yemen ( CNN ) -- Leaders of two tribal groups in Yemen say they will join protests demanding President Ali Abdullah Saleh 's resignation following violent crackdowns on demonstrators in Aden . `` 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 . `` We call on all those loyal to Yemen to stand with the revolution until this regime falls . '' The Yemen Solidarity Council is comprised largely of member of Saleh 's own Hashid tribe . Members of the Baqil tribe will also join in protests , according to Ahmar . But Saleh appeared to be standing firm , saying Saturday during a meeting with military leaders there was a plot against Yemeni unity , according to the official Saba news agency . The agency also said Saleh received pledges of support from sheikhs and local officials from Abyan Province during a meeting Saturday . Medical officials said Saturday that four people died and 26 were wounded -- some critically -- following clashes that erupted Friday night between anti-government protesters and security forces in southern Yemen . Amnesty International said at least 11 people had died in Friday 's protests , bringing the overall death toll since protests began to 27 . The international human rights group said that it has received reports that Yemeni security officials have prevented people from taking wounded people to the hospital . `` Events in Yemen are taking a serious turn for the worse and the Yemeni security forces are showing reckless disregard for human life , '' said Philip Luther , the group 's deputy director for the Middle East and North Africa . Witnesses said the victims of Friday 's violence were anti-government demonstrators hit by gunfire when security forces shot into crowds of protesters in the city 's Mualla district after 10 p.m. Friday . Yemeni government officials could not immediately be reached for comment . On Friday , authorities insisted no one had been killed in clashes in another part of Aden , but witnesses said one protester died of gunshot wounds and 11 demonstrators were wounded . The violence occurred after protesters gathered Friday across Yemen to demand Saleh 's resignation . Thousands of anti-government demonstrators -- mostly students -- lined the streets outside Sanaa University in the nation 's capital . They were countered by a pro-government demonstration on Tahrir Square , where thousands waved flags and held up pictures of Saleh , who has ruled Yemen since 1978 . The country has been wracked by a Shiite Muslim uprising , a U.S.-aided crackdown on al Qaeda operatives and a looming shortage of water . High unemployment has fueled much of the anger among a growing young population steeped in poverty . Demonstrators in recent anti-government protests have also cited government corruption and a lack of political freedom . Saleh has promised not to run for president in the next round of elections , and he has said he supports the creation of a national unity government to oversee upcoming parliamentary elections . Baqil tribal leader Faisal Dhalee said Saleh is making a mistake in trying to hang on . `` If the ruling party had some wisdom left , than it would quickly leave power , '' he said . Saleh he has refused to step aside immediately . On Monday , he compared the anti-government protests to an illness sweeping through the region . `` This is a virus and is not part of our heritage or the culture of the Yemeni people , '' he told reporters . `` It 's a virus that came from Tunisia to Egypt . And to some regions , the scent of the fever is like influenza . As soon as you sit with someone who is infected , you 'll be infected . '' Journalist Hakim Almasmari contributed to this report .
NEW : The Yemen Solidarity Council says security forces are blocking access to hospital . Medical officials say four people died and four were injured after clashes in Tunisia . Saleh tribal leaders say they will join protests calling for the Yemini 's resignation . Witnesses say the victims are anti-government demonstrators .