Indonesian police have officially declared jailed Muslim cleric Abu Bakar Bashir a suspect in terrorism cases, the attorney general's office said.

A defence lawyer said Bashir was now unlikely to be freed from prison on April 30 after serving a sentence for lesser offences.

"The Jakarta prosecutors' office has received a letter from police declaring the start of an investigation into Abu Bakar Bashir," attorney general's spokesman Kemas Yahya Rahman told AFP. This means Bashir has been declared a suspect, Rahman said. He did not know what case Bashir had been implicated in.

National police chief Da'i Bachtiar confirmed Bashir would be questioned as a suspect. "As to what his role is, it's still being investigated," he said.

The US and other foreign governments say the elderly cleric led the Al-Qaeda-linked Jemaah Islamiyah (JI) – the group blamed for the Bali nightclub bombings of October 2002, in which 202 people died, and for a string of other deadly attacks.

An appeal court had quashed Bashir's conviction for involvement with JI but confirmed a jail term for immigration offences and document forgery.

Defence lawyer Wirawan Adnan said he doubted Bashir would be freed as scheduled. Suspects can be detained for up to six months without charge in Indonesia under an anti-terror law.

"This shows that they are acting on orders from the United States. They are trying to satisfy the US at all costs. We suspect that the move is a kickback for something," Adnan told AFP.

Police indicated they have new evidence that Bashir headed JI. National detective chief Inspector General Suyitno Landung told local radio that Bashir would be interrogated as the leader of "an organisation which is discreet and secretive in nature." "Testimony from witnesses in Malaysia and Singapore shows there is a link between that organisation and Abu Bakar Bashir, who leads that organisation," Landung said without mentioning Jemaah Islamiyah.

The United States, Australia and Singapore all expressed disappointment after the Supreme Court in March halved Bashir's three-year prison sentence for the immigration offences.

Koran Tempo newspaper quoted an unidentified prosecution source as saying Bashir would be charged with involvement in several bombings along with Abu Rusdan, the self-confessed JI caretaker chief.

A Jakarta court in February jailed Rusdan for three-and-a-half years for shielding key Bali bomber Mukhlas from justice. The source said both men would probably be tried together.

A police spokesman said this month they would use testimony and statements from terror suspects detained in the Philippines, Thailand and Singapore in the Bashir probe.

The spokesman said police would also study transcripts of US interviews with top terror suspect Hambali, who has been in US custody since his arrest last August in Thailand.

Bashir, 65, denies the allegations as a Jewish and US plot to smear Islam. He was arrested in hospital a week after the Bali bombings but was never officially implicated in that case.

When his trial began in April 2003, prosecutors alleged he headed JI, authorised the network's church bombings in Indonesia which killed 19 people on Christmas Eve 2000 and plotted to blow up US targets in Singapore.

In September 2003 Bashir was convicted of taking part in a JI plot to overthrow the government but judges said there was no proof he had led the network. That conviction was overturned on appeal.

Bashir co-founded an Islamic boarding school in Central Java from which numerous convicted terrorists including some of the Bali bombers graduated.