Two journalists with the French news agency, AFP, and a photographer accompanying them are reportedly being held by forces loyal to the government of Libyan leader Moammar Gadhafi.
Reporter Dave Clark, photographer Roberto Schmidt and Getty photographer Joe Raedle have not been in contact with their office since late Friday.
The French news agency quotes the journalists' driver as saying he took the three men on Saturday from Tobruk along a desert road to Ajdabiya, where pro-Gadhafi forces were battling rebels.
He said the journalists were stopped by a convoy of military vehicles and then detained by soldiers.
On Monday, Libya's government released four New York Times journalists - almost a week after they were captured by pro-government forces while covering the rebel uprising in the country's east.
The released journalists include New York Times Beirut bureau chief Anthony Shadid, photographers Tyler Hicks and Lynsey Addario, and videographer Stephen Farrell.
In a story published in The New York Times on Tuesday, the journalists reported being treated harshly by pro-government forces. They reported being punched, bound, and butted with rifles by Gadhafi loyalists before they were ferried by air to Tripoli.
Several foreign journalists have been detained or disappeared in Libya since February 15, when the uprising against Gadhafi began.
On Sunday, Qatar-based television network Al-Jazeera said Libyan authorities arrested four of its journalists who had been working in western Libya. The network said "regional parties" are helping to secure their release.