WASHINGTON -- Austin Tice, an American freelance journalist covering the civil war in Syria who was last heard from in mid-August, remains unaccounted for and is likely being held by the Syrian government.

Statements in recent days by Czech diplomats, information from Syrian rebel supporters and reports from people inside Syria indicate that the 31-year-old Houston native, who contributed to McClatchy, The Washington Post and CBS News, was detained by Syrian government forces near the Damascus suburb of Daraya, his last known location.

The U.S. State Department says the Syrian government has not responded to inquiries about Tice that were made through official channels and that U.S. diplomats were “working through our Czech protecting power in Syria to get more information on his welfare and whereabouts.” A Syrian official in the United States declined to comment Thursday.

Tice entered Syria in May without a visa – a common practice for journalists attempting to cover the rebel side of the conflict there – and traveled throughout the country with rebel forces, reaching the Damascus area in late July. He remained in that area, basing himself in Daraya, a city of 200,000 southwest of Damascus proper, but had planned to leave Syria to meet friends in Lebanon on Aug. 19 or 20. He last communicated with colleagues on Aug. 13 but did not reveal precisely how he intended to exit Syria.

On Monday, the Czech ambassador to Syria, Eva Filipi, told a Czech television interviewer in Prague that sources had informed her mission that Tice was in detention, though further information had been hard to come by because of an Islamic holiday at the time. The Czechs, who oversee U.S. interests in Damascus because the U.S. closed its embassy there in February, sent a formal diplomatic note about Tice to Syrian counterparts, she said.

“Our sources report that he is alive and that he was detained by government forces on the outskirts of Damascus, where the rebels were fighting government troops,” Filipi said in response to a question about Tice. “Our additional steps were halted by the fact that the report came at the beginning of the final holidays of Ramadan and therefore we had a week off in Syria and some of our contacts were not in Damascus.”

The remarks followed a Czech radio report over the weekend that also said Tice had been detained by the government.

Since then, other information, gathered from a variety of people by the news organizations that publish Tice’s work, has provided support for that version of events.

One reporter who had met Tice previously said that rebels who had been with Tice expressed concern, saying he had left abruptly and not returned. The rebels were worried that he might have been taken captive, according to the reporter, who is not being identified out of security concerns.

Thursday, executives at both McClatchy and The Washington Post renewed their calls for information about Tice and urged his release if he is in Syrian government custody.

“We welcome any news about Austin, after three long weeks without word. He is a widely respected and dedicated journalist,” Anders Gyllenhaal, McClatchy vice president for news, said in a statement. “If he is in fact being held by the Syrian government, we would expect that he is being well cared for and that he will quickly be released.”