TRIPOLI, July 12 (Reuters) - Talks to release two Libyan journalists kidnapped in a former stronghold of ousted leader Muammar Gaddafi while covering the country's elections have broken down, the official mediating in the stand-off said on Thursday.

Since last year's uprising against Gaddafi, the interim government has struggled to control a myriad armed groups who refuse to lay down their weapons and often take the law into their own hands and detain people.

Reporter-cameraman Abdelqadir Fassouk and cameraman Yusuf Badi, who work for the Misrata-based Tobacts TV station, disappeared on Saturday near Bani Walid - one of the last Gaddafi strongholds to fall during the eight-month conflict.

"The Bani Walid group is steadfast in not releasing the two journalists," said Idris Al-Mismari, head of the state-funded Press Promotion and Support Board, who had been negotiating with the captors.

"We are calling on international bodies to intervene to seek the release of these two innocent journalists," Mismari told Reuters by telephone from Bani Walid.

The journalists had been covering Libya's historic election for a 200-seat national assembly in the western town of Mizdah and were on their way back to Misrata when contact with them was lost.

The collapse of talks on Thursday came hours before a deadline given by a militia in Misrata for their release was due to be reached. The militia had threatened to attack Bani Walid and free the men by force.

Attempts to contact the Misrata militia on Thursday went unanswered. Fighters there said on Wednesday the deadline for the release of the journalists had been set for 1.00 p.m. local time (1100 GMT) on Thursday.

Misrata was one of the first cities to join the revolt against Gaddafi and has a history of rivalry with Bani Walid. Local media said the captors of the journalists demanded the release of detainees in Misrata in return for freeing them. (Reporting by Ali Shuaib; Writing by Mark John; Editing by Pravin Char)