The head of information for the Jakarta police is quoted by the official Antara news agency as saying a training centre had been discovered at a university campus in the Jakarta satellite town of Tangerang.

Colonel Edward Aritonang said students were learning how to fire the catapults in preparation for protests after the Moslem fasting month ends in mid-January.

Some of the demonstrations have been violent

"The training was participated in by tens of students from several campuses and it was intended as a preparation for large-scale student demonstrations," he said.

The devices were being imported from Canada and the United States. Antara reported that some US catapults, known as "wrist-rockets", could be deadly.

"A person skilled in the use of a modern wrist-rocket can aim and fire the ball across a great distance, impacting on a target with nearly the same effect as a bullet fired from a 45 calibre pistol," it warned.

Clashes between student protesters and the security forces have become increasingly violent in recent months. At least 14 people were killed in November during a special session of Indonesia's highest legislative body.