Papua New Guinea police pledged Tuesday to use “any means necessary”, including “lethal force”, to free an Australian academic archaeologist and three others kidnapped in the country’s highlands.

At least four academics and guides from Australia and Papua New Guinea were taken at gunpoint in the country’s jungle-clad highlands early on Sunday.

Police Commissioner David Manning said air support and “other security elements” had been called in for an “operation to enable the safe release of the people involved.”

Papua New Guinea’s highlands are a sprawling expanse of jungle-cloaked hills where the central government and security forces have little sway.

In recent years, the region has seen an increase in tribal warfare and an influx of modern weapons.

The captors initially issued a ransom demand of roughly $1 million — an enormous sum in one of the Pacific’s poorest nations — before dropping the asking price and abandoning a 24-hour deadline.

“These are opportunists that have obviously not thought this situation through before they acted, and have been asking for cash to be paid,” said Manning.

“We are offering the abductors a way out. They can release their captives and they will be treated fairly through the criminal justice system, but failure to comply and resisting arrest could cost these criminals their lives,” he added.

“Our specialised security force personnel will use whatever means necessary against the criminals, up to and including the use of lethal force, in order to provide for the safety and security of the people being held,” Manning said.