Two Americans were among 19 suspected communist guerrillas who were killed in clashes with Philippine troops in a central province earlier this week, a government anti-insurgency task force said Saturday night.

The National Task Force to End Local Communist Armed Conflict said the Americans were killed, along with 17 other suspected New People’s Army guerrillas, in a series of clashes with army forces on 19 April in the coastal town of Toboso in Negros Occidental province.

The deadly fighting was first reported on Monday.

The task force warned Americans of Filipino descent in the United States to be wary of being lured by left-wing activist groups into joining or supporting Filipino insurgents in the Philippines in a recruitment process it described as “terror-grooming”.

The US and the Philippines have separately designated the New People’s Army as a terrorist organisation.

Human rights groups, however, called for an independent investigation into the clashes, saying that civilians were killed, including a student leader from the state-run University of the Philippines, two local advocates for farmers’ rights and a local community journalist who wanted to show support for impoverished villagers.

“We call on the international community to monitor this case closely, as it is not an isolated incident but part of a continuing pattern of International Humanitarian Law violations across the Philippine countryside,” the National Union of People’s Lawyers, a human rights group, said.

Undersecretary Ernesto Torres Jr, the executive director of the counterinsurgency task force, identified the two slain Americans as Lyle Prijoles and Kai Dana-Rene Sorem.

The US embassy in Manila did not immediately respond to a request for comment.

Torres said that all 19 people killed have been identified and their remains have been turned over to their families.

“These facts point to a disturbing convergence: foreign nationals in a live combat setting, where the risks are immediate and the consequences irreversible,” he said.

“The presence of two American fatalities in a single encounter should prompt careful reflection on how involvement in certain activities or networks may lead to unintended exposure to dangerous environments,” Torres said.

The two Americans arrived in the Philippines in March and “were believed to have subsequently travelled to Negros Occidental, where they were killed on April 19,” Torres said, without providing other details.

“Our thoughts are with their families, who now face the burden of loss under circumstances that unfolded far from their homes,” Torres said.

Military officials said the clash erupted as army troops responded to information provided by villagers about the presence of suspected rebels, and that a rebel commander with a bounty of 1 million pesos ($16,600) on his head was killed. A soldier was wounded in the fighting.

Troops seized 24 firearms at the scene of the clashes, and an unspecified number of fleeing guerrillas were captured, the task force said.

At its peak decades ago, the insurgent force had an estimated 25,000 fighters, who waged one of Asia’s longest-running communist rebellions.

Battle defeats, factional divisions and surrenders, however, have reduced the number of rebels to below 900, according to security officials.

Peace talks brokered by Norway collapsed under the previous Philippine president, Rodrigo Duterte, after both sides accused the other of continuing deadly attacks despite the negotiations.