LONDON Reuters correspondent Suleiman al-Khalidi was released by the Syrian authorities on Friday, three days after he was detained in Damascus.
A week after Syria expelled another Reuters foreign correspondent, Khalidi was set free to cross back into Jordan, where he is based, shortly after 4 p.m. (1400 GMT).
But Reuters had still had no contact with photographer Khaled al-Hariri, a Syrian based in Damascus, since he disappeared in the capital four days ago. He was last seen arriving at work on Monday morning.
A Syrian official has said the authorities were working to establish what had happened to him.
Reuters Editor-in-Chief Stephen Adler said: "Thomson Reuters is relieved that Suleiman is now free and has returned home.
"However, we remain deeply concerned about the whereabouts of Khaled and call upon the Syrian authorities again to help ensure his safe and timely return to his family."
Khalidi, a Jordanian who covered unrest which broke out in the Syrian city of Deraa two weeks ago, has worked for Reuters for more than 20 years, in Jordan, Kuwait, Syria and Iraq.
Hariri has worked in Syria for Reuters for more than 20 years.
Earlier in the week, two Reuters journalists from Lebanon were detained in Damascus and held incommunicado for two days before being released and expelled on Monday.
Reuters correspondent Khaled Yacoub Oweis, a Jordanian who had been based in Damascus for five years, was expelled from Syria last Friday for what a Syrian official described as his "unprofessional and false" coverage of events.
Reuters said it stood by its coverage from Syria, where the protests have posed the biggest challenge to President Bashar al-Assad's 11-year rule.
On Friday, witnesses said Syrian security forces killed at least three protesters in a Damascus suburb. And the state news agency acknowledged for the first time that worshippers in Deraa and Latakia, scenes of protests and deadly clashes last week, had gathered after weekly prayers to call for faster reforms.
A number of other Arab governments facing unaccustomed public opposition have taken action against the media this year.
On Wednesday, the Libyan government expelled a Reuters correspondent from Tripoli. Two weeks earlier, Saudi Arabia expelled the Reuters foreign correspondent from Riyadh.
Joel Simon, executive director of the New York-based Committee to Protect Journalists, said: "We documented over 300 individual attacks on journalists throughout the Middle East in the last several months and that's a conservative number.
"Circumstances differ in each case; repressive police action; attacks against individuals; but the aim is always the same -- to confront and control journalists trying to provide independent accounts in the country and to the world.
"That's what we're seeing across the region and Syria."
Reuters, part of New York-based Thomson Reuters, the leading information provider, employs some 3,000 journalists worldwide.
Reporting in English, Arabic and more than a dozen other languages, as well as providing video and photographs, it has had bureaux across the Middle East for well over a century.
(Editing by Alastair Macdonald)