Two local journalists are being held in a town known for its support of deposed ruler Muammar Gaddafi, a Libyan militia commander said.
The dispute is part of the overall lack of security in Libya, where rival militias and armed groups control various parts of the country in the absence of a strong central government and army.
Mohammed al-Swehili, a commander from Misrata, said his forces were giving the captors in the town of Bani Walid 48 hours to free the journalists.
If they are not released, he said, forces from all over the country would attack Bani Walid.
The two journalists work for Misrata's local TV station.
Bani Walid was one of the last pro-Gaddafi strongholds to fall in last year's civil war.