The United States urged Syria to confirm it is detaining an American freelance journalist who has been missing in the country for more than two weeks.
Austin Tice, 31, is believed to be held by forces loyal to Syrian President Bashar al-Assad, according to The Washington Post and McClatchy Newspapers, who called this week for his release.
"We have seen news reports that Mr Tice in Syrian custody," said Patrick Ventrell, a State Department spokesman.
"However, the Syrian government has yet to confirm these reports with our protecting power. We urge the Syrian government to respond... as soon as possible."
Ventrell said Washington was "concerned" about Tice's safety and well-being, and was working through the Czech mission, which has overseen US interests in Syria since the US embassy was closed in February, to get information about the reporter's location and well-being.
The Washington Post said Thursday that Tice was detained near the Damascus suburb of Daraya where activists say forces loyal to the Syrian president massacred hundreds of people last week.
McClatchy, a newspaper group, said Tice entered Syria in May without a visa, a common practice for journalists seeking to report on the war as Damascus issues few press visas. Many correspondents have crossed the border independently.
He then traveled throughout Syria with rebel forces, and reached the Damascus area in late July, setting up base in Daraya, which was pounded for days by Assad regime forces.
McClatchy said Tice last communicated with his colleagues on August 13, though he did not indicate how he planned to leave Syria.
Several foreigners, including at least one other American, have been detained by Syrian forces, the Post said.
Ten journalists have been killed since the Syria uprising began in March 2011, including five foreigners, according to the advocacy group Reporters Without Borders. At least 30 Syrian citizen-journalists have also been killed.