But with violence rising ahead of Tuesday's military handover from the Americans to Iraqis in major cities, the unit will need to pull off a difficult double: using every bit of its cutting edge to combat the insurgency while convincing Iraqis and the wider world it is squeaky-clean. The handover will almost certainly result in the country's numerous factions violently testing the will and ability of the government to manage without American troops on the streets. The commander of the Counter Terrorism Bureau insists his organisation is professional, non-sectarian and certainly not dirty. Army general Kalib Shegati al-Kenani says his force can cope with the challenge and that his country will not slide into renewed sectarian warfare. The elite units, armed with the latest US-made equipment, often pair up with American special forces to go after Iraq's most wanted foes: both al-Qaeda extremists and Shi'ite militants. They are thought to have been the main force that assisted the Americans during an offensive in Baghdad's Sadr City quarter last year to rout Shi'ite militias, and on operations targeting Sunni insurgents. Formed soon after the 2003 US-led invasion, the force became known as the "dirty brigade" because it was secretive and until recently operated outside the Iraqi chain of command, reporting directly to its US handlers. It was so little known that it was even rumoured to be used against the Shi'ite-dominated government's opponents in the political mainstream – a charge denied by the Iraqis and the Americans. Originally numbering about 4,500 members, it is reported to have doubled in size and now reports directly to Prime Minister Nouri al-Maliki. "We are professional and not sectarian forces, and we bring together people from all sections of the population. Each member of the bureau signs a document vowing not to speak about sectarianism, partisan affairs and nationalities. Their commitment is only to Iraq," al-Kenani said. Al-Kenani, a 59-year-old veteran of the eight-year Iran-Iraq War and the first Gulf War, is a Shi'ite, his deputy is a Sunni and one of his top generals is a Kurd. The force has sought to reinforce its non-partisan make-up by refusing to accept recruits who previously served in sectarian militias. Also, says Major General Abdul-Wahab al-Saedi, a senior commander, it "does not allow any minister or government official to enter its headquarters, to prevent any interference in investigations and security operations". Its ranks are made up of Shi'ites, Sunnis and Kurds, al-Saedi said, but it does not publish breakdowns. A statement in Arabic posted on the US military's website acknowledged the public's "misconceptions about this very viable and important unit". It picks its targets on the basis of rigorous checks, the statement said. "In short," it added, "the CTB's mission is targeting terrorists, not the Iraqi public or political foes." Al-Kenani said the bureau has a good intelligence-gathering machine and "cooperation with all ministries". The Americans are already leaving the towns and cities, and once they are gone, full responsibility will fall to the Iraqi police and military, which at last count numbered 654,362 members. Although some troops will remain as trainers and advisers, the remaining 133,000 US military personnel will be confined to base unless called in by the Iraqis. A full withdrawal is envisioned by the end of 2011. The Iraqi government has declared Tuesday a public holiday. "30 June is considered an Iraqi victory day and we will all celebrate the withdrawal of American forces," al-Kenani said. Explosions around the country have claimed more than 160 lives since 20 June, when a truck bomb in the northern city of Kirkuk killed 82. A bombing in Baghdad's Shi'ite district of Sadr City killed at least 61 people on Wednesday. Yesterday a motorcycle bomb killed a civilian and wounded four others in Baghdad's south-western district of Risala and a roadside bomb wounded three people in the city's northern Mustansiriya district. But al-Kenani said the days of near-civil war were over. "Whoever carries out explosions and security breaches after the withdrawal of forces will have no excuse," he said. "They were repeatedly bragging about fighting the occupation; now the occupation is out." US President Barack Obama also sent out a clear message that the recent spate of violence should not be allowed to push back the withdrawal. "If you look at the overall trend, despite some of these high-profile bombings, Iraq's security situation has continued to dramatically improve," he said. Of bigger concern than the violence, Obama said, is the lack of movement on laws to share oil revenues and other matters that keep Iraq deeply fractured along sectarian lines. He called on al-Maliki to step up his leadership. Yesterday al-Maliki insisted his country was on the road to peace and stability. He said: "We are on the threshold of a new phase that will bolster Iraq's sovereignty. It is a message to the world that we are now able to safeguard our security and administer our internal affairs. "We have high trust in our security forces to administer security and pursue al-Qaeda remnants and criminal gangs." He added that Iraq had achieved comparatively good levels of security, not just through better policing but also efforts at political reconciliation between Iraq's divided factions – something his critics often accuse him of dragging his feet on. He said: "If they (militants] want to bring down the political process, we say, it won't collapse, unless national unity is shaken." But yesterday the country's Sunni vice-president admitted he was worried about the deteriorating security situation. Tariq al-Hashimi called for people to avoid crowded areas and for Iraqi security forces to beef up their presence in public areas, markets and mosques before the 30 June withdrawal. Meanwhile, sceptics argue that Obama himself is too eager to get out of Iraq. They claim his determination to free up US troops so they can concentrate on fighting the Taleban in Afghanistan is putting at risk the undoubted gains made in Iraq. Some military analysts believe that despite the significant improvements in the training and equipping of Iraqi forces, and the existence of the Counter Terrorism Bureau, the country is still not ready to fight its own battles. Complicating matters further is the health of the Shia leader Abdel Aziz al Hakim, who has been vital in reducing the levels of violence after the US troop surge of two years ago. He is being treated for cancer in an Iranian hospital and his prospects do not look good.