Jakarta - A leading US human rights group on Tuesday denounced a series of disappearances of student activists demanding that President Suharto quit.

Human Rights Watch said in a statement sent to Reuters that senior army and police officers may have lied when they denied knowledge of missing students who later turned out to have been in their custody.

The alternative was that a secret military or paramilitary unit was operating without the knowledge of top-ranking officers, it said.

"Either way, the disappearances reflect badly on the Indonesian government," it said, calling on the authorities to find and prosecute those responsible.

"It is clear that the abductors of the disappeared political activists systematically and repeatedly violated Indonesian law," Sidney Jones, executive director of Human Rights Watch's Asia division, said in the statement.

"How can the government expect students or anyone else to respect the law or the authority of the state when state security forces themselves engage in such flagrant human rights violations."

At least 14 student activists have been reported missing since anti-Suharto protests began in February, just before he was re-elected to a seventh five-year term by a body he largely handpicked.

On Tuesday, the Legal Aid Foundation said three student activists reported missing since March 12 had been freed.

The students, Faisol Reza, Herman Hendrawan and Raharjo Waluyo Jati, all aged 24, were freed on Sunday, Foundation official Munir told Reuters.

"I received a telephone call on Saturday night from someone who did not identify himself that the students will be released on Sunday," he said.

"I then called the homes of Reza and Hendrawan on Sunday morning and found that it was true," Munir added.

Munir said the duo would not tell him who had picked them up or where they had been held, but did say that Jati had also been released. Munir said he had not been able to contact Jati.

Reza and Jati are student activists at Gadjah Mada University in Yogjakarta while Hendrawan is at Airlangga University in Surabaya, both cities on Indonesia's main island of Java.

On Monday, Pius Lustrilanang, 30, a student activist who disappeared on February 3 and subsequently resurfaced on April 4, told a news conference he had been kidnapped, beaten and subjected to electric shocks.

Pius said the powerful armed forces should take responsibility for his detention. Army chief General Wiranto has said no senior officer has ordered any abductions.

The student protesters blame Suharto for Indonesia's worst economic crisis in decades.

Security have forces tolerated demonstrations on campus, but have cracked down on students who have tried to take their protests to the streets, using tear gas, rubber bullets and canes. There have been no reports of death or serious injury.