MAIDUGURI, Nigeria (Reuters) - Suspected Islamist fighters went on the rampage in northeast Nigeria overnight, killing 10 Christians with guns and machetes and burning down their houses, witnesses said on Sunday.

The attack happened in a village called Chibok, in a remote part of northeastern Borno state, at the heart of an insurgency led by Islamist sect Boko Haram.

"Suspected Boko Haram came at night and set people's houses on fire before killing their victims," said Nuhu Clark, a former local councilor of the village who escaped the attack.

He said he counted ten bodies afterwards.

A police spokesman said they were aware of the incident but were still trying to confirm casualties.

Islamist fighters have killed hundreds of people since launching an uprising against the government in 2009, the usual targets being security forces, government officials or Christians, whom Boko Haram sees as infidels.

But the insecurity the conflict has created has also enabled criminal gangs who are nothing to do with the sect kill and rob.

In a separate incident, militants burned down three churches on Saturday in Gamboru, also in Borno state, said trader Umar Abubakar, who witnessed the attack.

Such attacks on Christians seem calculated to ignite sectarian tensions in Africa's most populous nation, which is split roughly evenly between Muslims and Christians. They mostly live side by side in peace, although bouts of violence between the communities sometimes flare up.

Boko Haram, which wants to carve out an Islamic state in northern Nigeria, has been blamed for more than 1,000 deaths since its insurgency intensified in 2010. The United States has designated three of Boko Haram's senior members as terrorists.

Its leader Abubakar Shekau praised jihadist movements across the globe on Thursday in a new video, and singled out the United States, Britain, Israel and Nigeria as enemies.

(Reporting by Ibrahim Mshelizza; Writing by Tim Cocks; Editing by Sophie Hares)