A grenade attack in the Kenyan coastal city of Mombasa Friday left four people seriously wounded, including a local chief, a government official said."A grenade from a speeding vehicle was thrown into a local chief's compound in Ngombeni, injuring the chief and three other people," the official, Margaret Mwaniki said."We are yet to establish the motive of the attackers," Mwaniki said adding that police were still hunting them.The area is a stronghold for the Mombasa Republican Council (MRC), a separatist group that was outlawed up until recently.It was in Ngombeni that MRC chairman Omar Mwamnuadzi was arrested on October 15 in a police raid that left two dead.Mwamnuadzi was freed on bail Monday.A local official was stabbed to death just after Mwamnuadzi's arrest, with the police attributing the murder to MRC sympathisers who suspected the official had tipped off police to the MRC leader's presence.The MRC was outlawed in 2010, a decision that was recently overturned by a Kenyan court.