Kampala - Rights groups on Monday urged Ugandan security forces to show restraint as they violently crackdown on tribal militia in a remote area near the Democratic Republic of Congo.More than four dozen people have been killed in clashes since Thursday, most of them guards protecting a tribal king who is critical of Uganda's long-time President Yoweri Museveni. The militia, armed with modern weapons as well as spears and machetes, have killed more than a dozen police officers in an escalation of a long-simmering conflict between the central government and a remote kingdom known as Rwenzururu.The Ugandan security forces "must not jettison human rights in their handling of the clashes" in the western Kasese district, said Amnesty International in a statement on Monday."The full picture of the weekend's events is yet to emerge, but there appears to be shocking examples of unlawful killings and a complete disregard for human rights during the arrests," said Abdullahi Halakhe, Amnesty's East Africa researcher. "In a shocking display of heavy-handedness, many people appear to have been summarily shot dead and their bodies dumped."Maria Burnett, an Africa researcher with Human Rights Watch, said that "everyone, including government troops and their commanders should face investigations into their conduct that led to the deaths."Gunfire rang out outside the palace in Kasese on Sunday as Ugandan troops tried to disarm King Charles Wesley Mumbere's guards and arrest him. Ugandan security forces overwhelmed the guards, broke into the palace and arrested Mumbere. In the process they may have killed an unknown number of the king's supporters.Ugandan opposition leader Kizza Besigye on Monday described the killings as a "massacre" and posted a photo purporting to show bodies of victims outside Mumbere's palace.'Senseless violence'"God save our country from this senseless violence," he said.Mumbere is king of Uganda's Bakonzo people and some of his supporters have been calling for secession from Uganda, according to Ugandan government spokesperson Colonel Shaban. Bantariza, who said he had seen copies of money printed by the secessionist group, which is hoping to create a republic known as Yiira.Mumbere denies being the commander of the separatists.The killings on Sunday have shocked many in this East African country that has had one president since 1986. Although tribal leaders and traditional monarchs only have ceremonial powers, the attack on Mumbere's palace is widely seen as a humiliating event among his followers. Television footage showed Mumbere being led to a police station as a soldier jerked him by the trousers. He is still in detention at an unknown location.President Museveni, who took power by force three decades ago, has struggled to win over the support of the Bakonzo people in presidential elections. There are frequent land disputes in the area, with many accusing the government of sponsoring land grabs. A new plan to divide up Kasese into two parts has also been fiercely opposed.In the 1990s, the area was the scene of a violent insurgency by the Allied Democratic Forces, a rebel group that now is based in DRC after being forced out of Uganda.