Al-Jazeera news channel says Syrian authorities have confirmed the detention of one of its reporters missing since Friday.
Dorothy Parvaz traveled to Syria on Friday to report on the political turmoil there.
Parvaz works for the English-language arm of the news network. She holds U.S., Iranian and Canadian citizenship and was once a reporter and columnist for the Seattle Post-Intelligencer.
Al-Jazeera called on Syrian authorities to release Parvaz immediately. Parvaz's detention highlights the worsening relations between Syrian authorities and the Qatar-based channel.
Al-Jazeera reporters were allowed to stay in Syria as other reporters were expelled several weeks ago, but last week the station said it was scaling back its Syrian operations, citing harassment by security forces.
Meanwhile, Syria on Wednesday promised to end its military operation in the southern city of Daraa, where its forces are besieging the anti-government protesters that sparked a wave of demonstrations across the authoritarian nation.
The announcement came even as elsewhere across the country, security forces made sweeping arrests to blunt the protest movement's momentum.
President Bashar Assad, whose army deployed tanks and snipers more than a week ago to crush dissent in Daraa, said in published remarks that the operation would end "very soon."
Daraa, near the Jordanian border, has been under siege since April 25 when Assad sent in the military, who cut off electricity and telephone service. Snipers have fired at residents who ventured outdoors and security forces shot holes in rooftop water tanks — vital for residents of the parched region.
About 50 people have been reported killed in Daraa over the past 10 days.
"The mission of the army units that entered Daraa on the 25th of last month will end very soon," Assad said, according to the private Al Watan newspaper. The paper did not give further details about the plans.
Later Wednesday, Syrian state television quoted an unnamed military official as saying the army was still "pursuing some armed terrorists" and was overseeing the end of its Daraa operation.
The uprising in Daraa was sparked by the arrest of teenagers who scrawled anti-regime graffiti on a wall. Protests spread quickly across the nation of some 23 million people.
Activists on Wednesday said military reinforcements and tanks were being sent to the central city of Homs. The area is another hotbed anti-government protests.
Residents said there was a heavy security presence and there were many arrests in the city, in a clear effort to intimidate any would be protesters.
Assad, who inherited power from his father in 2000, is determined to crush the six-week revolt, the gravest challenge to his family's 40-year dynasty.
Rami Abdul-Rahman, head of the Syrian Observatory for Human Rights, said Wednesday that 553 civilians have been killed since the uprising began. Dozens of soldiers have been killed as well, according to the state-run media.
Syria blames the unrest on a foreign conspiracy and "terrorist groups" that it says have taken advantage of protests.
Assad has acknowledged the need for reforms, and he has offered an amnesty to Syrians who turn themselves in before May 15 for carrying weapons or undermining national security.
But his overtures have been coupled with a brutal crackdown.
On Wednesday, a coalition of local committees helping to organize the protests said prisons were overflowing with detainees, forcing security forces to release people — "but only after those detainees have been subjected to the worst and most violent forms of torture."
The Syrian Coordinating Committees said that at least 500 people were being arrested daily.
Despite the crackdown, thousands of protesters staged a demonstration in the coastal town of Banias, calling for freedom. An eyewitness said the protesters were outraged over the arrest of seven elderly people the day before.
In Damascus, about 150 students gathered outside Damascus University's School of Economics, singing the national anthem and carrying banners that reads: "Lift the siege on Daraa," activists said.
Security forces attacked the demonstrators with batons to disperse them and detained two students. Ammar Qurabi, who heads the National Organization for Human Rights in Syria, said at least three students were arrested.
Qurabi added that security forces fired tear gas and live ammunition late Tuesday in Aleppo, Syria's largest city, to disperse students also calling for an end to Daraa's siege. He said several students were wounded, one in serious condition.
Students of Damascus University distributed an internet-based statement announcing their solidarity with the "legitimate demands of freedom and justice."
It was not clear how many of the thousands-strong university body supported the statement, but it was significant as one of the few statements in support of Syrian demonstrators that came from the country itself — and not from activists living abroad.