Banda Aceh – Indonesia's president is under threat of assassination, his spokesman said, amid stepped-up security nationwide for the New Year holiday period over fears of extremist attacks.

Security forces in the world's most populous Muslim nation have been on high alert over the Christmas period, concerned of possible reprisal attacks after last month's killing of Malaysian bombmaker Azahari Husin, a key member of the Jemaah Islamiyah (JI) militant network.

Documents found in Azahari's East Java hideaway indicated extremists were planning attacks over the holiday period. His chief accomplice, Noordin Mohammad Top, remains on the run.

Asked whether reports that President Susilo Bambang Yudhoyono was under threat of assassination were correct, his spokesman Andi Mallarangeng responded: "Yes." "We received the information from the intelligence agencies," he told AFP. "According to the report, the information is quite valid and they have a reason to believe it," he said.

Yudhoyono's outdoor activities had been "significantly reduced" by his guards until the situation improves.

National deputy police spokesman Anton Bahrul Alam told AFP that police had not yet received any intelligence report which suggested threats had been made on Yudhoyono's life.

"One clear thing is that we are on full alert status to anticipate various attack threats, including possible threats on the president's safety," he said.

JI has been blamed for a slew of attacks in Indonesia, including the 2002 Bali bombings, which killed 202 people, mostly Western holiday-makers.

Yudhoyono led a ceremony Monday to mark the one-year anniversary of the Indian Ocean tsunami and mingled freely with grieving survivors, although a press conference he was supposed to hold was cancelled without explanation.