Police freed the girl after three hours of negotiations. She came away with minor cuts.

The man held Saranlak Munikorn, a social science student, as she was walking from a woman's toilet.

He took her into the men's toilet and pointed the cutter at her neck.

A security guard called police who rushed to the scene and negotiated with the man who insisted he would only speak with reporters.

The stand-off drew hundreds of students to the library building, which was also the site where a move to solicit signatures for a petition to oust Thaksin was being conducted.

Talking to reporters, the man called himself "Hut" and issued documents requesting protesters to cancel the rally and hold talks in Parliament instead.

A part of the document read: "If you rally, I'll kill. If you stop, I'll let [the hostage] go".

After three hours, a special police force raided the toilet and helped the frightened hostage to safety.

Chiang Mai Police Commander Maj-General Jirut Prommobon said it was not thought the man was drunk or on drugs.

They were not sure, however, about his mental condition until he had been checked by doctors.

"Initially, he said he did it because he was upset with the anti-government rally and couldn't find anywhere to express his opinion," he said.

The man's identity remains a mystery. His identification card called him Teethanutnarittha Saowaphakchotiros, aged 39. But he carried other cards which identified him under other names.

After being charged, he told reporters he had been a salesman peddling credit cards and had been exploited many times before.

Only the PM can help poor people who are being exploited, he said.

The man was charged with unlawful detention and causing injury.

In the attempt to rescue the hostage, a table set up to solicit signatures for a petition to oust Thaksin was removed.

A forum to discuss the issue was also cancelled, said Somchai Prechasilpakul, a lecturer. "We want to relieve the tension because Saranlak's safety is more important than the issues."