By Kirsty Needham
SYDNEY (Reuters) -A police operation is underway to rescue an Australian university professor and three researchers taken hostage in the remote highlands of Papua New Guinea, the Pacific island nation's police commissioner said on Monday evening.
Armed criminals have demanded cash in return for releasing the captives, who included one foreign citizen and three Papua New Guinea students, Police Commissioner David Manning said in a statement, describing the gunmen as "opportunists" and the situation as "delicate".
"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.
The professor is an archaeologist who works for an Australian university and was on a field trip to the remote village of Fogoma'iu in the Mount Bosavi region, two sources with knowledge of the incident told Reuters. His companions - local researchers and a project manager from the capital Port Moresby - had also been taken hostage on Sunday, they said.
Police said the hostages were being held near Fogoma'iu at the boundary of Southern Highlands and Hela provinces.
Prime Minister James Marape told local reporters on Monday morning that police and the military were on stand-by as the government worked with missionaries who were acting as mediators.
The professor has not been publicly identified because of the sensitivity of the situation.
An earlier police statement had said there were "a number of foreign citizens" among the hostage group, which included academics and local guides. Manning's statement said there was one foreign national among the four hostages.
The criminals had come from Komo in Hela, spotted the university group by chance and took them into the bush, police said.
Manning said the abductors were being offered "a way out" and would face court if they released the hostages, "but failure to comply and resisting arrest could cost these criminals their lives".
Australia's Department of Foreign Affairs and Trade did not respond to requests for comment.