One British journalist has gone missing in Libya and two others are apparently in the custody of Colonel Muammar Gaddafi's forces.
Experienced foreign correspondent Dave Clark, 38, has not made contact with his editors at the Agence France-Presse (AFP) news agency since Friday evening.
He sent an email saying he and colleagues planned to interview refugees and leaders of the opposition to Gaddafi in the Tobruk region of eastern Libya the next day.
Denis Hiault, AFP's London bureau chief, said: "It's now been three days so we are pretty worried.
"We have quite a few people on the ground trying to find anything about their whereabouts. We don't know where they are, if they have been arrested or what."
The British reporter went missing with AFP photographer Roberto Schmidt, 45, and Getty Images photographer Joe Raedle.
Clark is originally from north-east England, where he worked for the Newcastle Evening Chronicle, and previously headed AFP's bureaux in Baghdad and Lagos in Nigeria.
He moved to AFP's Paris headquarters in September 2008 and has been reporting from Libya since 8 March.
Meanwhile, British Al Jazeera cameraman Kamel Atalua is being held by the Libyan authorities in the capital Tripoli along with three colleagues, the news channel has said. British reporter Stephen Farrell, who works for the New York Times, was also held by Gaddafi's authorities, along with three colleagues last Tuesday.
The New York Times reported on Friday that the four were set to be released by the Libyan government - but since then there has been no further news.
Guardian reporter Ghaith Abdul-Ahad was released from captivity by the Libyan authorities last week after having been missing for a fortnight.
Two weeks ago three BBC Arabic journalists were detained and repeatedly beaten by the Libyan security forces after being accused of spying.