A grenade attack on a church in a police compound in eastern Kenya has killed one police officer and injured at least 11 other people, reports say.The man who died was serving as pastor of the targeted church, in Garissa town near the border with Somalia.Most of the wounded are also reported to be police officers; some of whom were airlifted to hospital in Nairobi.In July, 15 people were killed in raids on churches in Garissa, and suspicion fell on the al-Shabab militant group.Police blamed the Somalia-based group and its sympathisers for the attack, and said they were angry over Kenya's role in a UN-backed intervention force.Kenya's capital Nairobi and the port city of Mombasa have suffered a series of grenade attacks since Kenya sent troops into Somalia last October.'Confusion'Witnesses were quoted as saying that the grenade in Sunday's attack was thrown from outside the compound, and landed on the iron-sheeted roof of the church while the officers and their families were inside attending a prayer session."It is believed to be a motor thrown or a grenade because it penetrated the roof before landing within the crowd. There is confusion," one police officer at the scene was quoted by Kenya's The Standard as saying.Gunfire was also reportedly heard at the scene of the explosion.Kenya's Red Cross said 11 wounded people were taken to hospital in Garissa, with three evacuated by air to Nairobi for further treatment.Regional police chief Philip Tuimur said a major operation was under way to track down the attackers.No group has yet claimed responsibility for the attack, but suspicion will once again fall on al-Shabab.In September, one child was killed and three seriously injured in a grenade attack on a church in Nairobi.A mob later rounded on Somalis living near the church, injuring 13 people with sticks and stones.