Philippines army soldiers ride in trucks into the fighting zone in Marawi City. File picture: Jorge Silva/Reuters

Manila - Six police officers were killed on Monday in a mistaken encounter with government troops who were on an operation against communist rebels in an eastern Philippine province, police said.

Nine police officers were also wounded in the 20-minute firefight with army soldiers in the town of Santa Rita in Samar province.

The officers were on patrol after receiving reports of armed groups in the area, said Chief Superintendent Mariel Magaway, a regional police director.

The army was also conducting an operation against the New People's Army, the armed wing of the rebel Communist Party of the Philippines, for the past five days in the area, he said.

"Both sides were caught by surprise and that is what happened, there was an encounter," Magaway said.

Major General Raul Farnacio, commander of the army division that covers the area, said the police and the military were working together in an investigation to determine what caused the "unfortunate incident."

Farnacio said it appears that the soldiers mistook the police officers as communist rebels. "When you are in a highly vegetated area, it's hard to distinguish who you are up against," he said.

"As we sincerely condole with the families of our brothers in the police, we assured the bereaved families that appropriate actions will be taken if there be any lapses committed (by) either side," he said in a statement.

"This is to ensure that the incident will not happen again," he added.