Washington – US and Indonesian officials believe hundreds of al-Qaeda fighters trained last year at a camp in central Indonesia, and fear sleeper cells could soon become operational there, the Washington Post reported Friday.

Officials in Jakarta have formally denied the existence of foreign terrorist training camps on Indonesian soil, but intelligence and government officials have said privately that al-Qaeda operatives ran a camp last year on Sulawesi island.

The camp was located in a thick jungle near the port city of Poso, and run by members of Osama bin Laden's network with the assistance of local Muslim extremists, the paper said, quoting Indonesian officials.

The fighters may have entered the country by posing as aid workers – Indonesian officials estimate that hundreds of foreigners, primarily from Europe, Pakistan and the Middle East, used that cover to reach the Sulawesi camp, the report noted.

Some carried a letter from a Muslim charity saying they were travelling to Sulawesi to rebuild mosques, but officials later discovered that the charity was linked to bin Laden and al-Qaeda, it said.

A senior Indonesian intelligence official said the camp was no longer operational.

Officials in both countries also believe al-Qaeda is linked with the country's largest and most violent Muslim militia, the Laskar Jihad, and another group, the Laskar Mujahedin, both fighting in Christian villages in the Moluccas.

But the leader of the Laskar Jihad has denied the claims, saying he refused financing from a top bin Laden aide last year and an offer of alliance with al-Qaeda, the Post reported.

Despite the mounting evidence, both US and Indonesian officials have said tracking the range of al-Qaeda activity in the country could prove difficult, the report said. The Indonesian archipelago consists of some 17,000 islands.

"We know they're here," the senior Indonesian intelligence official said. "We just haven't found them." One US official said the number of al-Qaeda members in Indonesia at present remained unclear. "We know they have come and gone, and it seems clear they'll be back again," the official said. "But are they here now? Have they set up sleeper cells here? We still are not sure."