At least three policemen and an airman were killed and 24 other people injured, four of them seriously, in Indonesia’s easternmost province of Papua during a clash Thursday with native people and university students, who have been demanding closure of a goldmine run by a U.S. company.

National Police Spokesman Anton Bachrul Alam told reporters protesters threw stones at security personnel and slashed them with machetes in front of the Cendrawasih University in Jayapura, the provincial capital.

Two of the three slain policemen were members of the Mobile Brigade elite police unit.

"The three policemen were earlier taken hostage inside the university’s compound by the mob," Alam said, adding that some of the injured policemen are currently in critical condition, mostly with head injuries.

The spokesman said police found evidence that the protest was well prepared. A car was found on the scene with many homemade bombs, machetes and arrows inside, he said.

Asked about possible involvement of the separatist Free Papua Movement in the incident, Alam replied, "As the incident took place at the Cendrawasih University, it is surely connected to university students."

Protests demanding for the closure of PT Freeport Indonesia, a local unit of New Orleans-based Freeport-McMoran Copper & Gold Inc., have been going on in the past few days in the province, demanding closure of the mining operation and withdrawal of soldiers deployed to secure it.

In a hastily arranged press conference, President Susilo Bambang Yudhoyono expressed regret over the incident and said the government is currently evaluating the operations of Freeport, including taxes and royalties, environmental damage and compensation to local communities in Papua.

"What we regret is while this process is still undergoing, there is this escalation of student elements and others (involved in the protests)," he told reporters.

The president said it appears that recent protests against Freeport have been "switched" to focus on the issue of independence.

"It is already clear that Papua is a legal territory of Indonesia. The international community, including the United Nations, has given their support to the fact that Papua belongs to the Republic of Indonesia," he said.

Asked about the demanded closure of Freeport, Yudhoyono said that it is legally impossible to just close down the company. "The investment climate can be disrupted (and) the cooperation can be harmed if there are legal uncertainties," he added.

The Freeport mine, the world’s largest gold mine and third largest for copper production, has long had an uneasy relationship with locals, many of whom are poor.

Over the past three decades, Papua has frequently been the scene of violence between separatists and government security forces that has claimed thousands of lives.

Rebels of the Free Papua Movement, who are fighting for an independent state, have kidnapped many locals and foreign nationals in an effort to gain international attention and support.

Indonesia took over the western half of New Guinea Island from the Dutch in 1963 and incorporated the territory into Indonesia after a 1969 plebiscite.

Papua is home to some of the world’s largest gold and copper mines and also has extensive forest reserves.

Jakarta has attempted to dampen separatist sentiment by offering Papua’s people a greater say in provincial-level government. It has also offered provincial authorities a larger share of local forestry, fishery, oil, gas and mining revenue.