At least 630 people have been killed in sectarian violence in Nigeria, the Red Cross said.

A senior official for the international aid organisation, speaking from the site of a mass grave in the central town of Yelwa, said that a Christian militia had attacked a Muslim community there.

As thousands of Muslims fled the town yesterday, Muslim leaders accused Christian militias of "genocide".

Last night residents in Yelwa showed journalists a 15 square metre (square yard) stretch of freshly disturbed soil where they said that they had buried 280 people who had been shot and hacked to death in a surprise attack by ethnic Tarok Christian militants on Sunday.

Although police deployed reinforcements to Yelwa where some residents took up machetes and cutlasses to defend themselves, a second round of fighting in the town on Tuesday afternoon left an unknown number killed, Yakubu Haruna, a town councillor, said.

"So many dead bodies," in the two attacks, the councillor said. "I cannot say how many."

Sotonye Wakama, an assistant police commissioner, said yesterday that he knew of just 67 dead. Another police officer, Raymond Nyama, said that 80 people were confirmed killed.

The killings are part of a cycle of conflict in Nigeria's central region since an outburst of Muslim-Christian violence in September 2001 pitted Christians against Muslims in the once-peaceful city of Jos. More than 1,000 people died in one week then. Many more have been killed since, including hundreds since January this year.

Abdulkadir Orire, the leader of Nigeria's foremost Muslim group, Jama'atu Nasril Islam, said that at least 250 people were killed in Yelwa in what he charged was an attempt by majority Christians to drive minority Muslims from the temperate central plateau state of fertile farms and pastures.

Sam Mbok, a leader of the Evangelical Church of West Africa in the nearby city of Jos, denounced the attackers as "mostly" animists and other non-Christians. "The Christian church does not support this violence," Mr Mbok said.

In Yelwa attackers had used kerosene to burn several mosques and hundreds of homes and vehicles.

Sanusi Yusuf, a 40-year-old cattle dealer, told of seeing his brother shot dead as the two ran from attackers who surrounded the town during the first attack on Sunday. The attackers used rifles, shotguns and colonial-era muskets to shoot at anyone who ventured onto the street, he said.

Thousands of residents fled on Sunday carrying whatever few personal belongings they could. Thousands more were evacuated in government trucks, among them scores of men, women and children with machete and gunshot wounds.

Although motives for the attack were unclear, it happened a week after Hausa-speaking Muslims reportedly launched an assault on the Tarok village of Kawo, burning churches and inflicting an unknown number of casualties.

In February suspected Muslim Hausa militants armed with guns and bows and arrows killed at least 48 people in a church in Yelwa, driving most other Christians out of the town.

For decades, the majority Christian inhabitants and the minority Muslim population - mostly Hausa and Fulani tribespeople with origins farther north - had lived in harmony.

Religious, ethnic and political enmities have fueled outbreaks of communal bloodshed resulting in more than 10,000 dead since President Olusegun Obasanjo was first elected in 1999, ending 15 years of repressive military rule.