Violent attacks by mostly Muslim and Christian militias on each other's communities in Central African Republic are spiraling out of control, setting the stage for "large-scale massacres and counter-massacres," said Human Rights Watch's U.N. director.

Philippe Bolopion, who has just returned from Central African Republic, said no one seems to be pursuing any real political or religious agenda -- the warring parties are just looting, raping, killing and razing villages.

Now villagers have formed vigilante committees called the anti-balaka, meaning "anti-machete," to defend themselves -- but too often to retaliate against Muslim civilians, Bolopion said, leading to the prospect of "large-scale massacres."

"We have entered a cycle of massacres and counter-massacres by two armed forces who almost never face each other, but who kill civilians from communities they associate with their enemies," he told The Associated Press on Friday.

Secretary-General Ban Ki-moon, in a report released Friday, urged the Security Council "to explore the option of a possible United Nations peacekeeping mission in that country," in additional to an African Union force already in the country.

One of the world's poorest countries with a long history of chaos and coups, Central African Republic has been in turmoil since a coalition of rebel groups joined forces to overthrow the president in March and put their leader in charge.

Since seizing power, the Seleka rebels have plunged the country into a state of near-anarchy. They have also been accused by human rights groups of committing scores of atrocities, of widespread looting, killings, rapes and conscription of child soldiers.

About half of Central African Republic's 4.6 million people are Christian, and 15 per cent Muslim, with the others following indigenous religions.

In October, the Security Council unanimously backed a new African Union peacekeeping force and called for free and fair elections within 18 months. The AU force was established in July and currently has about 1,900 troops.

Central African Republic borders some of the most tumultuous countries on the continent, including Congo and Sudan, and some diplomats have expressed concern that even when it reaches its full strength of 3,600 troops the AU force would not be large enough to deploy beyond key population centres.

"It is clear that the African peacekeepers who are currently on the ground have not succeeded in stopping a cycle of vicious abuses committed by ex-members of the Seleka, as well as more recently activated anti-balaka militias," Bolopion said. "The deployment of a well-equipped and strongly mandated U.N. force would go a long way in bringing back a measure of protection for civilians."