COLOMBO, Sri Lanka (AP) - Suspected Tamil Tiger rebels hurled a grenade at police officers guarding a church in northwest Sri Lanka where hundreds of Christians were attending a Christmas service early Monday, killing a policeman and wounding three others, the military said.

The condition of one of the wounded was serious, the government's Media Center for National Security said.

The incident happened around 1:45 a.m. in northwest Mannar on Monday, as about 500 people attended a Midnight Mass service, an official at the center said.

The officer accused the attackers of trying to force security forces to retaliate with gunfire, which could have resulted in civilian casualties. He said the police did not return fire.

Hours earlier, a combined army-police security post came under grenade attack in Mannar town, said an officer at the media center, who cannot be named due to military regulations. No one was hurt.

Phone calls to rebel headquarters in northern Kilinochchi remained unanswered.

Sri Lanka's two-decade civil war ended in 2002 when Norway brokered a cease-fire, but the truce has come under serious threat due to an escalation of almost daily violence. This year, more than 3,500 combatants and civilians have been killed in violence, according to the Defense Ministry.

The rebels from the Liberation Tigers of Tamil Eelam say they are fighting to create a separate homeland for the country's 3.1 million ethnic minority Tamils, accusing the majority Sinhalese of discrimination.

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