MANILA--Ten Philippine police officers, who mistakenly shot at a vehicle and killed two of its passengers late Thursday, and a senior officer have been relieved of their duties, the capital's police chief said as he ordered an investigation into the incident.

Metro Manila's top officer Oscar Albayalde said the vehicle, which was carrying seven people, including a woman who had been shot earlier that night, was on its way to a hospital when police opened fire after mistaking it for one driven by the woman's assailant.

Albayalde said the police officers from Mandaluyong city, part of greater Manila, may have been given wrong information because they were told by village officials that the passengers of the vehicle were armed.

"We can't totally blame them," Albayalde told a media briefing.

Albayalde also relieved the chief of Mandaluyong police of his command pending the investigation.

"We are not hiding anything here. We're not discounting the possibility ... that there may be overkill or violation of our POP," Albayalde said, referring to Police Operational Procedures (POP).

Philippine police are already facing unprecedented scrutiny due to concerns about their conduct during anti-narcotics operations. Several opinion surveys have indicated dwindling trust of police accounts of operations that have killed close to 4,000 people.

Human rights groups and political opponents say executions of drug users and small-time peddlers have been widespread, but police insist those killed were all dealers who put up violent resistance.