US Secretary of State Hillary Clinton has urged Nigeria to arrest and try those responsible for killing hundreds of people near the city of Jos. The massacre is seen as revenge for a previous round of killings in January. Human Rights Watch says the violence has continued because no-one has been held accountable in the past and "it is time to draw a line in the sand". Nigerian troops are patrolling the villages which were targeted on Sunday in a bid to prevent further violence. Acting President Goodluck Jonathan has sacked the country's national security adviser, Sarki Mukhtar in an apparent response to the killings. Some have questioned how the attack could have taken place when a military curfew has been in place since January, when at least 200 people died in clashes between rival Christian and Muslim groups. Calm restored Christian leaders complained that it took the army two hours to react to a distress call. The Plateau State Christian Elders Consultative Forum told AFP news agency that by that time, "the attackers had finished their job and left". Many of the dead in the villages of Zot and Dogo-Nahawa, largely inhabited by Christian members of the Berom community, are reported to be women and children. The latest attacks are said to have been reprisals for the January killings when many victims were Hausa-speaking Muslims. The authorities say the villages are now calm after troops and military vehicles entered them. Mrs Clinton also urged the authorities to ensure that the army respected human rights as it restored order - Nigeria's security forces have a reputation for brutality. "The Nigerian government should ensure that the perpetrators of acts of violence are brought to justice under the rule of law, and that human rights are respected as order is restored," she said. "This kind of terrible violence has left thousands dead in Plateau State in the past decade, but no-one has been held accountable," said Corinne Dufka from US-based lobby group Human Rights Watch. Officials from the Christian-dominated state government say that up to 500 people were killed but others say the death toll might have been exaggerated. Dozens of arrests have already been made, say officials. Chief Gabriel Gyang Bot, from nearby Shen, told the BBC's Focus on Africa programme that people in his village feared more attacks. He said he had received text messages from people who claimed responsibility for the weekend attacks and had threatened to return. In January, religious leaders blamed inflammatory text messages for fuelling the violence. 'Traps set' Mark Lipdo, from the Christian charity Stefanos Foundation, said Zot village had been almost wiped out. He said: "We saw mainly those who are helpless, like small children and then the older men, who cannot run, these were the ones that were slaughtered." A resident of Dogo-Nahawa said that the attackers had fired guns as they entered the village before dawn on Sunday. Some witnesses said villagers were caught in fishing nets and animal traps as they tried to escape and were then hacked to death. Mud huts were also set on fire. Mass burials for the victims were held on both Sunday and Monday, officials say. Figures given for the death tolls in the ethnic clashes have varied widely, sometimes to achieve political ends or to reduce the risk of reprisals, or simply because victims are buried quickly. Plateau State and its capital, Jos, lie between the mainly Muslim north of Nigeria and its largely Christian south. Clashes have broken out periodically since 2001, with competition for resources and political power seen as being at the heart of the conflicts between the rival communities. The violence represent a challenge for Mr Jonathan. He formally took over last month from President Umaru Yar'Adua, who has a heart problem. Mr Yar'Adua returned from three months of treatment in Saudi Arabia two weeks ago but has still not been seen in public. Source: BBC