Five more bodies have been found in a third mass grave for victims of the Philippines election massacre taking the death toll to 57.

Police said the remains were in addition to six bodies found earlier in the day in a large pit buried with three vehicles - the second mass grave discovered since Monday's attack on an election convoy.

No suspects have been formally named.

President Gloria Macapagal Arroyo has been under local and international pressure to swiftly punish the attackers.

Police said they were investigating a member of a powerful clan along with four police officers.