MANILA >> Hundreds of rival Muslim rebels have clashed over land in the southern Philippines, leaving at least 13 dead and thousands of villagers displaced in the monthlong fighting, the military and rebels said Thursday.

The land feud, which has simmered for years, erupted into a new round of clashes Jan. 6 in North Cotabato province’s hilly township of Kabacan, pitting hundreds of fighters from two groups of Muslim insurgents that have been fighting for minority self-rule for decades, regional army spokesman Maj. Marlowe Patria said.

At least 13 people, mostly combatants, have been killed and nine wounded in the clashes between the Moro Islamic Liberation Front and the Moro National Liberation Front. About 3,000 villagers have fled to nearby townships, Patria said, adding that gun and mortar fire were still ongoing Thursday.

Government troops were not involved and have tried to pacify both sides, he said.

Leaders of both groups convinced the warring commanders to sign an accord to stop fighting on Tuesday but a new clash broke out a few hours later, said Eid Kabalu, spokesman for the Moro Islamic Liberation Front.

Such clan and land conflicts have flourished for decades in southern regions, fueled by large numbers of unlicensed weapons, weak law enforcement and political grievances.

The Moro National Liberation Front fought for a separate Muslim homeland in the country’s south until it settled for limited autonomy in a 1996 peace pact with the government. Many members, however, refused to disarm and still maintain rural strongholds.

The Moro Islamic Liberation Front broke off from the MNLF in the 1980s. It has waged its own fight for Muslim self-rule and entered into Malaysian-brokered peace talks with the government. It has observed a truce with government troops.