Indonesian troops are searching the West Papuan jungle after a deadly attack by gunmen at the weekend in which two US teachers and an Indonesian were killed.

The ambush took place near the world's biggest gold and copper mine - the American-owned Freeport mine, which has been criticised by activists for its impact on the local community - in Indonesia's easternmost province.

To find them is like to find a small needle in a soccer field

Major General Mahidin Simbolon

The Indonesian military blames the attack on separatist rebels in West Papua - formerly known as Irian Jaya.

But independence activists and human rights experts have cast doubt on the government's claims, saying the military could have staged the attack to gain support for its fight against the rebels.

The attack will undermine Indonesia's efforts to persuade international investors that the fragile archipelago is moving towards stability.

Rebels suspected

Saturday's incident was the worst ever attack in the province involving foreigners.

It took place on the road from the Tembaga Pura international school that serves mining operation staff, 3,300 kilometres (2,060 miles) east of Jakarta, to Freeport's main centre of Kuala Kencana.

Government officials said they suspected separatist rebel group the Free Papua Movement (OPM).

There has been a separatist rebellion in the province since the 1960s, but this is the first time foreigners have been targeted.

Military accused

One top human rights expert in West Papua, John Rumbiak, told the BBC's Jakarta correspondent Richard Galpin, he was convinced the Free Papua Movement was not behind the attack.

He said he had spoken to the main rebel commanders in recent weeks, who pledged not to target civilians of any nationality.

Investigators are examining the site

He also said he had spoken to a local tribal official who had driven past the spot where the attack took place about 30 minutes before.

He quoted the official as saying he had seen a group of men in full military uniform with automatic weapons standing at the side of the road.

Automatic weapons were used in the attack.

Survivors recovering

Indonesia's Major General Mahidin Simbolon has strongly denied that the military are to blame.

He said he was determined to find the attackers, but the local topography in the remote province would hamper efforts.

"It's jungles and ravines and mountains... To find them is like to find a small needle in a soccer field," Major Simbolon told Reuters news agency.

And survivors of the attack in the misty highlands did not see their assailants, said Geoff Hocking, the mine's town manager.

In addition to the three killed in the attack, at least seven foreigners and three Indonesians were wounded. The foreigners were reported to be school teachers and their families.