Jakarta – FBI agents have returned to Indonesia to investigate the killing last August of two American schoolteachers in restive Papua province, an issue Washington has said could seriously affect bilateral ties.

The United States said last month it had warned Indonesia "at the highest levels" over the ramifications should the world's most populous Muslim nation fail to cooperate over the murders.

A senior US official this week said the issue was of the "highest priority" to Washington, adding some problems that hindered a January FBI visit – such as the presence of military officials in interviews with witnesses – had been resolved.

The FBI team, put at five by police, met chief security minister Susilo Bambang Yudhoyono on Friday. It was unclear how long they would stay and if they would visit Papua.

Erwin Mappaseng, head of the police's criminal investigation division, said they had brought high-tech equipment to help. "The equipment includes technology on DNA matching ... We are still gathering and identifying evidence that can lead to the suspects who are still vague at this point," he said.

One Indonesian was also killed when gunmen sprayed a convoy of mainly American schoolteachers and their families with gunfire near a giant mine operated by US-based Freeport-McMoRan Copper and Gold Inc. No one has been charged over the killings.

Indonesian police have previously said some weapons used were of the same type as those carried by troops stationed nearby, but that it was too early to point fingers at the military.

The military has denied any wrongdoing in the attack near the copper and gold mine. The teachers killed worked at an international school serving the mine's expatriate staff. FBI agents have made one previous public visit, in January.

"It's imperative that we have closure and credible accountability for those killings," said the senior US official, who declined to be identified.

If any military hand were found it would likely jeopardise Jakarta's bid to restore normal military ties with the United States, slashed after bloodshed gripped East Timor's 1999 vote to break from Indonesian rule.

Soldiers provide the main security for Freeport's mine in Papua, where a low-level rebellion has simmered for decades.

The military has blamed Papuan rebels for the attack. They have denied any involvement. Some Papuan human rights groups say military elements could have staged the ambush to discredit the rebels or get higher payment for their security role. Papuans differ ethnically from most Indonesians, who are Muslim. Papuans are either Christian or animist.