Chiranuch Premchaiporn, who manages the Prachatai news website, was stopped Friday by immigration police at Bangkok’s international airport and shown an arrest warrant issued by police in the northeastern province of Khon Kaen. She had just attended a conference in Hungary dealing with online free expression.

She was released on bail shortly after midnight after being driven by police to Khon Kaen, 275 miles (445 kilometers) away, where the complaint against her was filed.

Chiranuch was arrested last year on similar charges, and both cases involve offending messages posted by readers more than a year ago on her site’s web board, for which she has been held responsible. She has not yet been tried, but faces up to 50 years in prison on the old charges.

"We call for Chiranuch’s immediate release and the withdrawal of the charges against her so that we do not have to witness another attempt to exploit the Computer Crimes Act to silence the regime’s critics," the Paris-based press freedom group Reporters Without Borders said in an e-mailed statement. "Prachatai is a reliable source of news and information that has managed in recent months to keep the public informed about what is going on in Thailand."

The New York-based Committee to Protect Journalists and human rights group Amnesty International both called for Chiranuch’s immediate and unconditional release.

"The government should stop using anti-crown charges to suppress legitimate criticism," said Shawn Crispin, CPJ’s representative in Southeast Asia.

Chiranuch said she was still hopeful for freedom of expression on the Internet in Thailand. "The arrest just showed some flaws or weaknesses that existed in the judicial process," she told The Associated Press.

Thailand’s freedom of speech reputation has taken a battering in recent years, as the government has tried to suppress political opposition that has sometimes turned violent. Its standing in the Press Freedom Index issued by Reporters Without Borders slipped to 130 last year from 65 in 2002, when the ratings were initiated.

The Committee to Protect Journalists said the arrest "comes amid an intensifying crackdown on Thai media." The government has shut down a satellite television news station, community radio stations, print publications and websites aligned with the anti-government advocates, it said.

Prachatai, which was established by several respected journalists, senators and press freedom activists, describes itself as an independent, nonprofit, daily Web newspaper that provides information "during an era of serious curbs on the freedom and independence of Thai news media."

Thailand’s lese majeste law mandates a jail term of three to 15 years for "whoever defames, insults or threatens the king, the queen, the heir to the throne or the regent." The 2007 Computer Crime Act carries a penalty of up to five years’ imprisonment and a fine of 100,000 baht ($3,260).

The act bars the circulation of material deemed detrimental to national security or that causes public panic, and authorities have used it to block thousands of websites deemed insulting to the monarchy.

Prachatai reported Saturday that Chiranuch was freed after posting 200,000 baht ($6,525) bail. She must report back to police in Khon Kaen on Oct. 24.

The complaint against her was filed by Sunimit Jirasuk, a businessman in Khon Kaen, in April 2008.