A group of local officials, some relatives of Maguindanao Gov. Esmael Mangudadatu, were inspecting a road project near Lake Buluan on Sunday when the rebels opened fire, triggering a gunfight that also left one guerrilla dead, said Mangudadatu and a military spokesman.

Muslim rebels killed 10 people, including supporters of a provincial governor, in fighting linked to a dispute over fishing grounds in a volatile southern Philippine region, officials said on Monday.

A group of local officials, some relatives of Maguindanao Gov. Esmael Mangudadatu, were inspecting a road project near Lake Buluan on Sunday when the rebels opened fire, triggering a gunfight that also left one guerrilla dead, said Mangudadatu and a military spokesman.

Mangudadatu’s wife and other relatives were among 58 people massacred by a rival clan in 2009 in the country’s worst election—related violence in recent history.

The province has been rocked by sporadic violence since the killings, with authorities believing that some of the suspected gunmen on the run have joined Muslim rebels who have been fighting for a separate homeland for decades.

Mr. Mangudadatu said that seven of his relatives and four local officials had just alighted from a motorboat to inspect the road project when the guerrillas opened fire.

About 100 Moro Islamic Liberation Front rebels took part in Sunday’s attack, said military spokesman Col. Prudencio Asto. Residents fled their homes and army troops took positions between the two sides to try to pacify them and prevent new clashes, he said.

“While our troops are there they will not clash. The problem is when our troops leave the area, they might resume fighting,” Col. Asto said.

Rebel leader Mohagher Iqbal said that guerrillas and villagers have been locked in a land dispute with Mr. Mangudadatu’s supporters and oppose the road project because they fear it will lead to the exploitation of the lake and nearby natural resources.

The rebels maintain an encampment near the lake but they have generally respected a cease—fire with government troops while their leaders have been involved in negotiations to end the decades-long insurgency.

Mr. Mangudadatu’s wife, relatives and other supporters were killed along with 32 journalists and their staff in the 2009 massacre in Maguindanao, about 560 miles (900 kilometers) south of Manila.

The main suspect, former town Mayor Andal Ampatuan Jr., surrendered days after the killings and has pleaded not guilty. Among the dozens of suspects in detention, 51 have been arraigned but more than 100 others remain in hiding.

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