There has been fresh violence in the riot-torn Kenyan city of Mombasa, with at least one explosion and a number of casualties reported.Details of the attacks are yet to be confirmed but they follow two days of rioting that have left four people dead, including three policemen.The riots were sparked by the killing of radical Muslim cleric Aboud Rogo Mohammed by unknown gunmen.He was accused by the US and UN of backing Islamist fighters in Somalia.Reports of the latest violence vary, but Agence France-Presse quoted the Kenyan Red Cross as saying one person had been killed and two critically hurt in a grenade attack.The Kenya Television Network spoke of two grenade attacks, with the second injuring "scores of policemen" in the Makupa suburb of the city.Associated Press news agency quoted police spokesman Kipkemboi Rop as saying that four policemen had been hurt when a grenade was thrown into a van carrying officers near the Mombasa Pentecostal Church.None of the reports has yet been verified. Al-ShababSome of the rioters had accused the authorities of being behind Mr Rogo's killing, saying he had been the victim of a "targeted assassination".However, police spokesman Charles Owino was quoted as saying that the Somali militant Islamist group al-Shabab killed the cleric in an attempt "to galvanise support among the youth".Two dozen people were arrested on Tuesday in the riots and were charged in court on Wednesday with taking part in an unlawful assembly and in a riot.They were remanded pending bail hearings.Mr Rogo was on US and UN sanctions lists for allegedly supporting the al-Qaeda-affiliated al-Shabab in neighbouring Somalia.The UN Security Council imposed a travel ban and asset freeze on him in July, saying he had provided "financial, material, logistical or technical support to al-Shabab".It accused him of being the "main ideological leader" of Kenya's al-Hijra group, also known as the Muslim Youth Centre, which is viewed as a close ally of al-Shabab.In 2005, Mr Rogo was cleared on murder charges over the 2002 attack on a hotel where Israeli tourists were staying, which killed 12 people.