Four New York Times journalists, including a Briton, have been reported missing while covering the fighting in Libya.
Editors last heard from them on Tuesday as they were covering the retreat of rebels from the town of Ajdabiya.
Libyan officials told the newspaper they were trying to locate the four, executive editor Bill Keller said in a statement.
The paper said there were unconfirmed reports that forces loyal to Libyan leader Muammar Gaddafi had detained them.
“We are grateful to the Libyan government for their assurance that if our journalists were captured they would be released promptly and unharmed,” Keller said.
The missing journalists include reporter Stephen Farrell who holds dual British and Irish citizenship.
In 2009, Farrell was kidnapped by the Taliban and later rescued by British commandos.
The other are Pulitzer Prize-winning reporter Anthony Shadid, and photographers Tyler Hicks and Lynsey Addario.
“Their families and their colleagues at The Times are anxiously seeking information about their situation, and praying that they are safe,” Keller said.
The White House urged the Libyan government to refrain from harassing or using violence against journalists. Obama spokesman Jay Carney said the United States is firm in its belief that journalists should be protected and allowed to do their work.
The advocacy group Reporters Without Borders said it was asking its correspondents in Libya to help track down the journalists’ whereabouts.
“It’s a very dangerous climate for reporters right now,” said Clothilde Le Coz, Washington director for Reporters Without Borders.
“It’s a reminder that these are real people, and they are putting themselves at real risk to bring information out of these places.”
All four Times journalists are experienced war correspondents.
In September 2009, Farrell and Sultan Munadi, an Afghan journalist and interpreter who worked regularly with the Times and other news organisations, were taken hostage when they went to cover the aftermath of a Nato air strike that killed scores of civilians in northern Afghanistan.
Munadi and a British commando Corporal John Harrison died in the raid that rescued Farrell.
An inquest was held in Salisbury yesterday into the death of Cpl Harrison, 29, from the Parachute Regiment, who led his unit out of a Chinook helicopter under heavy fire in the Special Forces-led pre-dawn operation.
Farrell was also kidnapped in 2004 in Fallujah, Iraq. He previously worked for the Times of London.
The Committee to Protect Journalists says it has documented five assaults, 25 detentions and dozens of attempts to obstruct or intimidate journalists as they try to cover Libya’s unrest.
Covering Libya has quickly become more dangerous for reporters than the earlier uprising in Egypt, said Joel Simon, executive director of the Committee to Protect Journalists. He said Egyptian President Hosni Mubarak had tried to preserve his international reputation by reining in government attacks on journalists.
“There’s no such calculation going on in Libya,” Simon said. “It’s a very difficult, precarious situation for the press right now.”
On Saturday Al-Jazeera cameraman Ali Hassan al-Jaber was killed and correspondent Baybah Wald Amhadi was wounded when their car was ambushed near Benghazi.
Last week three BBC employees were detained, beaten and subjected to mock executions by Libyan soldiers while attempting to reach the western city of Zawiya
Two weeks ago, Libyan authorities detained a Brazilian reporter and Ghaith Abdul-Ahad of Britain’s Guardian newspaper. Both were later released.