The 14 students arrested for staging a political gathering in defiance of the National Council for Peace and Order (NCPO) were ordered released on Tuesday by the Bangkok Military Court.
The court rejected a request by Samranrat police for permission to detain them for another 12 days for further investigation. (corrected: not military police as earlier)
The court's denial of an extension had been expected following pressure and criticism from several groups of rights advocates, both inside the country and abroad.
The students were arrested on June 26 on charges of defying an NCPO order issued under Section 44 of the interim constitution prohibiting a political assembly of five people or more, and for violating Section 116 of the Criminal Code.
The charges carry sentences of up to seven years in prison.
They were taken before the Bangkok Military Court on Tuesday morning and the police submitted a request for court permission to detain them for another 12 days.
The military court rejected the request on the grounds the students had not tried to flee and there was no reason to detain them further.
The court also said continued detention would make it difficult for the students to prepare their case to defend themselves in court.
Realatives and supporters expected the students would be freed later Tuesday, but it was later reported they would not be let out of prison before completing their 12th day in detention at midnight, and possibly not until Wednesday morning, to their great disappointment.
Although ordered released from detention, the students are still within the judicial process. If military prosecutors decide to arraign them they will stand trial in the military court.
Of the 14, the 13 male students were to be taken back to the Bangkok Remand Prison and the sole female student to the Central Women's Correctional Institution, where they would be officially released later today.
Earlier on Tuesday morning, a group of Thammasat University students, students of the New Democracy Movement, and relatives of the 14 students gathered in front of the court to give them moral support.
The detainees' relatives and lawyers were allowed into the courtroom, along with representatives from several embassies, including France, Germany, the US and Sweden. No reporters were allowed in court.
Metropolitan police from Chana Songkhram and Phra Ratchawang stations, both in plainclothes and uniform, as well as military police from the Office of the Permanent Secretary for Defence, were deployed inside the court compound to ensure law and order.