CAIRO - Libya’s intelligence body said it arrested a prominent local journalist, acknowledging the detention four days after his disappearance, which brought international criticism.

Journalist Reda Fhelboom disappeared after his arrival in the capital Tripoli from neighbouring Tunisia. He is founder of the Libyan Organization for Independent Media, which works to document rights violations against Libyan journalists.

Fhelboom’s disappearance Saturday drew the attention of local and international human rights advocates. On Monday, the Interior Ministry issued a statement denying any involvement in his arrest and accusing the intelligence services of holding him.

In an unprecedented move, Libya’s secretive intelligence body issued a statement Wednesday insisting that Fhelboom’s arrest met all legal standards and was co-ordinated with the country’s public prosecutor. However, the intelligence apparatus, which operates independently from the Interior Ministry, made no mention of what, if any, charges have been filed against Fhelboom. His whereabouts are unknown.

The U.N. Support Mission in Libya had called earlier this week for Fhelboom’s release and expressed concern that Fhelboom’s “arrest and detention may be on account of his work as a human rights defender and journalist,” in violation of international law.

Although the Tripoli-based government is backed by the U.N. and other Western countries, many of its institutions are in reality staffed and controlled by local militia groups. The intelligence agency is loosely aligned with Tripoli.

The Tripoli government has courted powerful militias for its protection. It’s been facing a months-long assault on the capital by forces loyal to a rival government based in Libya’s east. Those forces, led by commander Khalifa Hifter, have been trying to capture the capital since April.

Rights groups have repeatedly said that Libyan militias on all sides of the conflict have committed human rights abuses, including abducting activists, journalists and human rights activists.