A roadside bomb killed four American soldiers in Baghdad, the US military said Monday, as an upsurge of violence left 50 Iraqis dead, undercutting the prime minister's claim that government forces are prevailing over insurgents and sectarian extremists. The military had earlier reported the deaths of two other American soldiers on Sunday and one on Saturday, making it one of the deadliest weekends for the US military. More than 50 people were killed on Sunday in a wave of bombings and shootings across Iraq. In one of the deadliest attacks, a group of assailants in three cars opened fire at an open-air night market in Khalis, killing at least 12 people and wounding 25 others, police said. A government statement received Monday said that an explosion in downtown Baghdad killed eight people and injured 18 when a suicide bomber detonated himself on a minibus. On Sunday evening, two back-to-back suicide car bombings in the northern city of Kirkuk killed nine people and wounded 22, hours after another suicide car bomb killed one person and wounded 16. In Basra, Iraq's second largest city, a motorcycle bomb at a night market killed four people and wounded 15, the governor's office said. "We're not in a civil war. Iraq will never be in a civil war," said Prime Minister Nouri al-Maliki on CNN's "Late Edition," insisting that his government was combating attacks, "The violence is in decrease and our security ability is increasing."