Unidentified attackers lobbed grenades into a mosque in eastern Sri Lanka Friday, killing four men at prayer and wounding at least 25, local residents said.

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The blasts ripped through the mosque in the town of Akkaraipattu in the district of Ampara, 350 km east of Colombo by road, while hundreds of devotees were praying, a resident said by telephone.

He said the attack came a day after the Muslims in the area defied Tamil rebel pressure to boycott Thursday's presidential elections, which were marred by sporadic violence in the volatile eastern province.