A Norwegian court has jailed an Islamic radical in custody for four weeks for threatening a witness to change his testimony in a case involving recruiting people to fight in Syria.

Prosecutor Per Niklas Hafsmoe says Arslan Maroof, known as Ubaydullah Hussain, was apprehended on Tuesday after "an incident" last weekend.

Hussain, a leading member of local Islamic extremist group "The Prophet's Ummah," denied wrongdoing during Thursday's custody hearing at the Oslo District Court. Ummah is the Arabic word for the worldwide Islamic community.

He is suspected of recruiting fighters for the Islamic State group. He earlier had been acquitted of multiple counts of encouraging others to commit murder and acts of terrorism.

Hussain is being held in custody during the police investigation and will eventually be tried.