MANILA (Reuters) - A breakaway Muslim rebel group killed nine civilians in the southern Philippines in a series of attacks on Christmas eve, officials said on Saturday, in a reminder that the region remains volatile despite recent gains in the peace process.

Army troops killed four members of the Bangsamoro Islamic Freedom Fighters, a faction opposed to a peace deal between government and the mainstream Muslim rebel group, after they attacked a farming town in Sultan Kudarat province on the southern island of Mindanao.

Miriam Ferrer, the government's chief negotiator in peace talks with the Moro Islamic Liberation Front, said seven farmers were shot at close range while working in their rice paddies and two other civilians were killed in a grenade attack on a chapel in nearby North Cotabato province.

Ferrer said the rebels had also taken civilian hostage in the Sultan Kudarat attack and used them as human shields when soldiers pursued them, but the hostages were later freed.

The Bangsamoro group broke away from the main Muslim rebel group in 2011 to fight for the creation of an Islamic state in the south of the mainly Catholic country, a goal shared by another small militant group, Abu Sayyaf, which has gained notoriety for bombings, beheadings and kidnappings of foreigners in the western part of Mindanao.

The ceasefire with the main Moro Islamic Liberation Front is holding, however, while both the government and communist guerrillas declared a 12-day ceasefire from Dec. 23 nationwide to mark the Christmas and New Year's holidays. On Saturday, the Maoist-led rebel group is also celebrating its 46th anniversary.

Security forces are on heightened alert around shopping malls, churches, bus stations and ferry terminals during the holidays to guard against possible attacks.

Police officials said the group behind the Christmas eve attacks in Mindanao had pledged allegiance to Islamic State militants in the Middle East in videos posted to YouTube but they had no evidence linking them directly to militants from Islamic State in Iraq and Syria. They also had no evidence that any Filipinos had traveled to the Middle East to fight with IS.

In March 2014, the Philippines signed a peace deal with the main Muslim rebels granting the minority Moro people autonomy in exchange for dismantling the 11,000-strong guerrilla army and turning over their weapons, ending a 45-year conflict that killed 120,000 people and displaced 2 million.

(Reporting By Manuel Mogato; Editing by Edmund Klamann)