Four New York Times journalists who were covering the conflict in Libya were unaccounted for Wednesday and are feared missing, the newspaper said.

The journalists include Anthony Shadid, a veteran Middle East correspondent who won two Pulitzer Prizes for foreign reporting as a Washington Post reporter.

The Times identified the other journalists as Stephen Farrell, a reporter and videographer; and photographers Tyler Hicks and Lynsey Addario.

While reporting for the Times in Afghanistan in 2009, Farrell was kidnapped by the Taliban and held hostage before being rescued by British commandos.

All four of the journalists have worked extensively in the Middle East, the Times said.

Times editor Bill Keller said the four were last seen by other journalists as they were covering the retreat of rebel forces from Ajdabiya, heading toward the rebel stronghold of Benghazi.

“There’s some speculation that they were stopped at a Libyan government checkpoint, but we don’t know yet,” Keller said, adding that he thought the four were traveling together.

Many western journalists entered Libya earlier this month through Egypt, crossing a border held by rebels. None of the journalists who entered the country this way had visas or other entry papers, which left them vulnerable to detention from the Libyan police or military. However, reporters in Tripoli, Libya’s capital, entered the country with permission.

The Times reported that the newspaper has contacted officials in Tripoli, who are assisting in the efforts to locate the four.

“No one knows too much,” said Sudarsan Rhagavan, who is in Libya for The Washington Post and was with the Times reporters on Tuesday. “We came under heavy bombardment on the western edge of Ajdabiya. Everyone ran. I last saw Anthony running to his car. We were all safe from the shelling, I believe.”

Rhagavan headed to another site and, later in the day, left for Benghazi. The Times reporters were believed to have been staying at a house in Ajdabiya when Moammar Gaddafi’s forces entered the area in late Tuesday afternoon.