Manila: The Philippine president has ordered police to investigate alleged state-sponsored death squads blamed for killing more than 800 suspected criminals in a southern city, a senior official said Wednesday.

New York-based Human Rights Watch reported last month that its investigation showed that some police and government officials provided training and weapons to hit men who gunned down 814 suspected drug dealers, petty criminals and street children allegedly involved in gangs between 1998 and February 2009 in Davao city.

Thirty-three killings were reported in January alone, the group said.

President Gloria Macapagal Arroyo's government has also come under severe criticism from international rights groups and a UNinvestigator on extrajudicial killings for the deaths of hundreds of left-wing activists allegedly by security forces.

The government has denied any involvement and said the figures are bloated and that some of the political killings may have been carried out by communist rebels. It has put up a reward for information leading to the arrest of those responsible.

Ermita said Arroyo directed the Department of Interior and Local Government and the Philippine National Police to first determine the existence of death squads and prosecute perpetrators.

He urged witnesses to "come forward and be heard" but warned that "there is no room for hearsay evidence."

Kenneth Roth, executive director of Human Rights Watch, said last month that police "consistently fail to bring the perpetrators to justice, while the local government cheers from the sidelines."

National police chief Jesus Verzosa has denied the killings were state-sponsored.

Davao Mayor Rodrigo Duterte has blamed the killings on gang wars and drug addicts.