(CNN) -- Two French journalists working for Europe1 are missing in Syria, the French radio station said Friday, prompting fears that they may have been kidnapped.
Reporter Didier Francois and photographer Edouard Elias were on their way to the northwestern city of Aleppo when they went missing, the radio station said.
Europe1 is in constant contact with the authorities to make every effort to get more information, it said.
French President Francois Hollande told reporters at a news conference in Tokyo that contact had been lost with the two journalists, although it was not yet clear in what circumstances.
He called for them to be "released immediately" because they are not representatives of any state, according to video broadcast by CNN affiliate BFMTV.
"They are men who work so that the world can receive information," he said.
Didier Francois is an experienced war reporter while Elias has previously worked in Syria, the broadcaster said.
The two were making their way to Aleppo from Turkey, it said.
An Amnesty International report published last month named Syria as the most dangerous place in the world for journalists.
The report highlighted serious abuses committed by both government and opposition forces against professional and citizen journalists, both Syrian and international.
A number of foreign journalists have disappeared in Syria.
The Italian daily newspaper La Stampa said Thursday that it had confirmation that its reporter Domenico Quirico, who disappeared there on April 9 while on assignment, is alive.
Quirico, made a short phone call to his wife, La Stampa said. The Italian foreign ministry confirmed in a statement that contact was made between Domenico Quirico and his family.
The Brussels evening newspaper Le Soir said that Pierre Piccinin de Prata, a Belgian academic and political scientist who was reporting for the paper, disappeared in Syria in May, Reporters Without Borders said.
An American freelance reporter, James Foley, has been missing in Syria since November 22, 2012. His brother and the GlobalPost, an online international news outlet to which Foley contributed, said last month that they believe he is most likely in Syrian government custody.
U.S. freelance journalist Austin Tice disappeared in mid-August 2012. Bashar Fahmi, a Jordanian correspondent with al-Hurra television channel, went missing the same month.
According to the Committee to Protect Journalists, 45 journalists have been killed in Syria since the beginning of the conflict in March 2011.
CNN's Pierre Meilhan and Alexander Felton contributed to this report.