Baghdad was rocked by mortar fire and a suicide bombing on Wednesday (December 6), just hours before a report by a U.S. panel called for U.S. forces to withdraw from combat over the next year. The bipartisan Iraq Study Group said no timetable should be set for a full pullout of some 140,000 U.S. troops but says U.S. forces should now focus on supporting the fledgling Iraqi military. Insurgent violence demonstrated the scale of the task facing an Iraqi force itself beset by sectarian tensions. A suicide bomber wearing an explosive belt blew himself up inside a bus in a Baghdad Shi'ite slum, killing four people and wounding seven others, police said. But an Interior Ministry source said that three people were killed and 16 others wounded in the blast that took place in Sadr City. The blast turned the bus into a complete wreckage. "A bomb inside a bus coming from Gayara went off here," said an eyewitness A bomb inside a shop killed its owner and three others and wounded 12 in the town of Iskandariya, 40 kilometres (25 miles) south of Baghdad, police said on Wednesday (December 6). "We left our houses from the early morning to work and earn living. We are vendors who used to sell oranges and (different kinds of fruits). A bomb exploded (inside a shop). It was planted inside salt bags." Mortar rounds landed in residential Sunni neighbourhoods of northern Baghdad late on Tuesday (December 5), killing four civilians and wounding 14 others, police said. They said that five mortar rounds landed in al-Seleikh district of northern Baghdad, killing two and wounding 11, while the other mortar rounds landed in al-A'dhamiya district, killing two and wounding four others. Iraq is gripped by tit-for-tat sectarian killings between Shi'ite and Sunnis and many Iraqis fear their oil-rich nation passed the point of no return into sectarian division after the destruction of a Shi'ite shrine in February. Outside Siniya, a town besieged by U.S. troops for nearly a week according to the mayor, more emergency food aid waits to allowed through military checkpoints. Two days ago, residents said the Americans were preventing aid convoys from entering and people from leaving the town after militants forced the mayor and entire police force to resign. The provincial governor, Hamad al-Qasey, welcomed U.S. efforts, saying "we do not want the people of Siniya to be victimised by these groups." On Wednesday locals said food was being allowed in.