PORT MORESBY, Papua New Guinea (AP) _ Australia has impounded a plane reportedly carrying helicopters, missiles and other weapons to Papua New Guinea for use by foreign mercenaries hired to quash an island rebellion.

Controversy over Papua New Guinea's $36 million deal with Sandline International, a British-based mercenary firm, forced Prime Minister Julius Chan to resign this week in order to cool civilian and military protests.

Army soldiers, who opposed the contract saying they themselves are underpaid and ill-equipped, detained about 70 British and South African mercenaries and deported them.

A caretaker prime minister was appointed Thursday and the government is investigating Chan's deal with Sandline, which some military leaders allege was corrupt.

On Thursday, Australian air force jets intercepted a cargo plane in airspace between northern Australia and Papua New Guinea, according to reports in today's Sydney Morning Herald and Sydney's Daily Telegraph.

It was not clear why military supplies were being flown to Papua New Guinea, since nearly all the mercenaries were deported a week ago.

A spokesman for Australian Defense Minister Ian McLachlan told reporters today that the cargo plane was diverted at the request of Papua New Guinea and that Australia had been asked to hold onto the cargo.

``The Papua New Guinea government was concerned about the delivery of the material to Papua New Guinea under the circumstances and asked Australia to store it. So we did,'' the spokesman said on customary condition of anonymity.

The plane landed at Tindale air force base in the Northern Territory where the cargo was placed under guard, he said. The Herald reported that plane later took off for an unspecified Asian destination. It was not clear from where the plane originally took off.

Officials at the base declined to comment on the reports. Papua New Guinea government officials were not available for comment.

The Sydney newspapers said the Russian-made Antonov AN-124 aircraft carried several attack helicopters, military vehicles, and an arsenal of weapons, including heat-seeking missiles, grenades, 500 cases of ammunition, explosives, and rockets.

The defense ministry spokesman would only confirm helicopters were part of the cargo, citing security reasons for refusing to comment further.

Papua New Guinea has been fighting separatist rebels on Bougainville, a copper-rich island 800 miles northeast of Port Moresby. The rebellion began in 1988 as an environmental protest, then escalated into a secessionist war. About 1,000 people have died in the fighting.

Acting Prime Minister John Giheno, a member of Chan's Cabinet, said he would only govern temporarily and hoped to give the job back to Chan within a few weeks.

Giheno said if the Chan was exonerated by a government inquiry into the mercenary deal ``he comes back,'' possibly before June's general election.

Sandline chief Tim Spicer, a former British army officer, is the only mercenary still in Papua New Guinea. He is awaiting trial on April 8 for charges of possessing an unlicensed pistol and ammunition.