Nine bodies were found by police near Wennapuwa town some 50 kilometers north of the capital.
"When nine bodies are found together its obvious that they have been murdered, but we are still awaiting details," he said.
Unexplained killings have increased in Sri Lanka since hostilities escalated between government troops and separatist Tamil Tiger guerrillas in December 2005.
Since then, bodies some burned beyond recognition and some headless and naked, apparently to conceal their identities, have been recovered from different parts of the country, most of them outside the north and east, where the fighting is concentrated.
On March 3, police found five bodies in a marsh near the town of Kandana, north of Colombo, while three days later five burned bodies were found near abandoned cultivation land in north-central Anuradhapura district.
Over 5,000 people have been killed in violence in the past 19 months despite a Norway-brokered cease-fire in place.
Tamil Tiger rebels are fighting the government to create an independent state for the country's ethnic minority Tamils who have suffered decades of discrimination by successive Sinhalese-majority governments.
A 24-year separatist war has claimed over 70,000 lives.