Gunmen from a shadowy cult have ambushed a group of police officers in central Nigeria, killing 23 of them and then setting fire to their bodies, the state's police chief has said.

The police said on Thursday that the attack was an ambush in Nassarawa state and the suspects belonged to an armed group called Ombatse.

"The Ombatse gunmen opened fire on our men, killing 23 and burning them," Nassarawa state police chief Abayomi Akeremale said, adding that 17 officers remain missing.

Ombatse is 'very much alive'

Nassarawa roughly falls on the dividing line between Nigeria's mostly Christian south and predominately Muslim north.

One of the state's major ethnic groups, the Eggon, is divided between the two faiths, but also has a history of links to pagan movements.

Ombatse, which means "time has come" in Eggon, has described itself as a movement committed to purging society of certain vices, including alcohol and adultery.

The police chief said the security forces had tried to arrest some Ombatse leaders following allegations of forced conversions in the village of Elakyo, not far from the state capital Lafia.

"We decided to send our men to the area to arrest members of Ombatse including their priest," he said.

"(They) have been going to churches and mosques initiating people into their cult by forcefully administering an allegiance oath to unwilling people."

Shadowy group

The group has operated in the state for several years but its size has been hard to quantify.

The male members of the group are said to dress only in black, while women are reportedly barred from many of the major ceremonies.

Until recently, incidents of violence were limited.

Last November, Ombatse gunmen were reported to have shot dead three security personnel in a shootout with troops who stormed a shrine during an initiation ceremony.

Days later, in an apparent reprisal for the raid on their shrine, purported Ombatse gunmen killed 10 members of a rival group while destroying several homes.

Nassarawa Governor Tanko Al-Makura in December launched a probe into the activities of the Ombatse following the unrest.

Several Nigerian dailies on Thursday reported that Al-Makura had travelled to the capital Abuja to brief security officials on the latest violence.

"We discovered a certain militia group holding arms and carrying out cult activities," he was quoted as saying in the Punch newspaper.

"This thing has not abated and in the past two weeks it took a total different dimension."

Nigeria, Africa's most populous country, includes some 250 ethnic groups.

While Christianity and Islam are dominant, various other religious and spiritual movements are present across the country.

Nigerian media frequently carry reports of crimes related to the occult, but the details are often murky.