ABU GHRAIB, Iraq (Reuters) - The United States handed over control of all combat duties to Iraqi security forces on Saturday in a further sign its withdrawal is on track despite a political impasse in Iraq and a recent rise in violence. US President Barack Obama said last Monday he would stick to his promise to end US combat operations in Iraq by August 31, with security being left in the hands of Iraqs own US-trained army and police. Today is an extremely important day as we continue to progress towards turning over full responsibility to the Iraqi security forces, General Raymond Odierno, top commander of US forces in Iraq, told reporters after a departure ceremony for the last US combat brigade. Seven years after the US-led invasion to topple Saddam Hussein, Washington is reducing the number of troops in Iraq to 50,000 by September 1 from just under 65,000 currently and close to 150,000 during the height of the conflict. During the ceremony, a division of the Iraqi army demonstrated vehicle checks and other security measures often employed in the war-battered country, where bombings and other attacks remain daily occurrences although overall violence has subsided since the conflict peaked in 2006-7. While this was the last combat brigade to hand over control to Iraqi forces, there will still be six brigades left in the country after US combat troops leave by the end of the month. The six Advice and Assist Brigades, which come into effect from September 1 when the US moves formally into an advisory role, will train and support Iraqs army and police. However, the inability of Iraqs fractious parliamentary parties to come up with a coalition government five months after elections has created a power vacuum potentially vulnerable to sectarian tensions and left many Iraqis concerned about the ability of local forces to maintain security. There was a sharp rise in deadly attacks in July, increasing fears that insurgents are trying to exploit the political situation to foment sectarian strife. The Iraqi security forces have continued to do their job throughout this time and have not been affected at all by the delays in the formation of the government, Odierno said in Abu Ghraib on the western outskirts of Baghdad. Iraqi Defence Minister Abdel Qader Jassim, who also attended the ceremony, said the issue of politicians struggling to agree on a coalition government was a political one and that the primary responsibility of Iraqi forces was to protect Iraqis. American forces have been patrolling in a support role with their Iraqi counterparts for months and US commanders say the remaining force of 50,000 at the end of this month will be enough to counter any unexpected surge in violence.