Burundi police fired tear gas and beat protesters who were demanding President Pierre Nkurunziza end his bid for a third term, in a resurgence of unrest has stoked fears of ethnic conflict in Africa's Great Lakes. A Reuters photographer said at least eight of the flag-waving and chanting demonstrators were dragged off by police on Tuesday. Some in the crowd responded by pelting officers with stones and rocks.Rights groups say at least 20 people have died in three weeks of clashes between security forces and protesters who say Nkurunziza's ambitions violate the constitution and a peace deal that ended an ethnically fuelled civil war in 2005.Laying the same charges against the president, a group of renegade generals tried and failed to overthrow him last week. The government said late on Monday it would treat any future demonstrators as accomplices in the failed putsch.But crowds gathered again in the capital's suburb of Nyakabiga on Tuesday, shouting: "We will not stop until he gives up the third term."Diplomats say the longer unrest continues the more chance that a conflict, which up until now has been largely a struggle for power, reopens old wounds in a region with a history of ethnic killing.South Africa said earlier on Tuesday next month's election should be postponed indefinitely until political stability had returned, as regional leaders scrambled to contain the impasse and a potential humanitarian crisis."NO TO COUP"More than 110,000 people -- many of them Tutsis -- have fled to neighbouring Rwanda, Democratic Republic of Congo and Tanzania, where cholera has been found among thousands of refugees sleeping rough on the shores of Lake Tanganyika, waiting evacuation by boat.The failed coup has heightened fears the crisis in the landlocked nation of 10 million could split the army, the central pillar of post-war unity between Hutus and Tutsis.Until recently, Nkurunziza, a former rebel leader with mixed parentage, had also been seen as bridge between the main groups in a region that has been an ethnic powder keg for the last half-century.Neighbouring Rwanda, which shares a similar ethnic mix, suffered a genocide in 1994 in which 800,000 people, mostly Tutsis and moderate Hutus, were killed.The protesters in Bujumbura stressed they were against both Nkurunziza and the attempted coup, and denied any links with the plotters."No to the coup, and no to the third term. We will continue until he says no to the third term," one of the demonstrators, who gave his name as Jean-Paul, told Reuters. He did not wish to give his last name, for fear of reprisals.The government said on Tuesday it had no desire for extra-judicial vengeance."The people implicated in the disgraceful attempt to overthrow legitimate institutions will be arrested and prosecuted by justice, and only by justice," it said.Nkurunziza says his participation in elections does not violate the constitution as his first term does not count because he was appointed by parliament, not chosen by a popular vote. ..