NAIROBI, Nov 28 (Reuters) - A Kenyan court on Wednesday summoned the country's police chief after the family of a man in custody on suspicion of belonging to the fearsome Mungiki gang asked for his release.

The family of John Mwangi Kiruthi, 22, say he was arrested by police in a village on the outskirts of the capital Nairobi in July and is being held incommunicado in an unknown place.

Rights activists accuse Kenyan police of killing hundreds of members of the murderous terror gang during a crackdown this year. But police deny carrying out any extrajudicial killings.

"I hereby summon the Commissioner of Police and Attorney General to appear in court tomorrow to show cause why the suspect should not be released," Judge George Dulu ruled after hearing the family's application.

The Mungiki gang terrorised central Kenya earlier this year with a spate of beheadings and murders. That prompted a government sweep during which scores of suspects were gunned down by the police in two raids on a Nairobi slum.

Human rights groups accuse the police of executing suspected gang members then dumping their bodies in grasslands near the capital after a Nairobi morgue filled up.

"Kiruthi has been in police custody for over 90 days at an unidentified location with (no) access to his family," lawyer Victor Kamau said in court papers he filed at the high court.

"The family is therefore anxious about his safety since he is being held illegally," he added.

Mungiki, made up mainly of men from the Kikuyu tribe, started as a religious sect espousing a return to traditional values, but later metamorphosed into an violent extortion ring.

Police could not immediately comment on Kiruthi's case. (Reporting by Robert Hummy; Writing by Helen Nyambura; Editing by Giles Elgood)

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