Bombings in the lead-up to the pullback of U.S. forces from Iraq's towns and cities resulted in the bloodiest death toll seen in the conflict-hit nation in 11 months, official figures showed Wednesday.
Some 437 people were killed in June, government ministries announced as Iraqi forces officially took charge in the country's urban areas a day after the pullout of American troops six years after the invasion.
U.S. President Barack Obama, who opposed the 2003 war ordered by his predecessor George W. Bush, hailed the U.S. withdrawal as an "important milestone" but warned of difficult days of bloodshed and violence ahead.
A car bomb attack on Tuesday at a popular market in Kirkuk, an oil hub which has long been riven by ethnic tensions, killed 33 people and wounded 92 others, underscoring the residual unrest that plagues Iraq.
The problem was boldly restated by June's casualty figures, which showed that 372 civilians, 45 policemen and 20 soldiers died in violence nationwide - the highest toll since July 2008.
Prime Minister Nuri al-Maliki warned last month that insurgents and militias were likely to step up attacks ahead of the June 30 handover deadline, in a bid to undermine confidence in Iraqi security forces.
The deadliest attack this year occurred near Kirkuk on June 20 when 72 people were killed.
Iraq had marked the American pullback on Tuesday with a national holiday six years after the invasion which toppled Saddam Hussein but sparked an insurgency and sectarian bloodshed that left tens of thousands dead.
Further military parades took place on Wednesday in Kirkuk and the restive northern city of Mosul.
"This is a great day," said Kirkuk police chief Major General Jamal Taher, insisting Tuesday's attack would not dent the resolve of his officers, or blight the significance of the security handover.
"Explosions will not decrease the determination of Kirkuk police. On the contrary, it will increase our strength," he said.
Iraq's 500,000 police and 250,000 soldiers are now in charge in cities, towns and villages, while most of the 133,000 US troops remaining in the country will be based outside towns and cities.
The Americans will largely play a training and support role ahead of a complete pullout ordered by Obama by the end of 2011.
Maliki on Tuesday took on critics of Iraq's security forces, saying they were up to the task of taking over from the Americans.
"It is an offence to the Iraqis. The people who said that the foreign troops would never withdraw and would keep permanent bases in our country were giving a green light to the terrorists to kill civilians," he said.
The U.S. military said four soldiers died from combat-related injuries on Monday, taking to 4,321 the number of American troops killed since the invasion.
"Make no mistake, there will be difficult days ahead. We know that the violence in Iraq will continue; we see that already in the senseless bombing in Kirkuk earlier today," Obama said at the White House on Tuesday.
"This is an important step forward, as a sovereign and united Iraq continues to take control of its own destiny," he said, adding that Iraqi leaders now had to make "hard choices" to resolve political issues and bolster security.
Obama has asked Vice President Joe Biden to oversee the U.S. departure from Iraq and Washington's effort to promote internal political reconciliation.
U.S. Defence Secretary Robert Gates said Tuesday he expects "sporadic attacks" as Al Qaeda fighters "increase the level of violence to try to pretend that they forced us out of the cities."
The top U.S. commander General Ray Odierno told U.S. reporters he believed Iraq was now better off "not having a dictator such as Saddam Hussein".
But he declined to say how many U.S. troops would be left in urban centres.
Tuesday's pullback was part of a security pact signed in November setting the terms for a continued U.S. military presence in Iraq.
The Status of Forces Agreement says U.S. commanders must now seek Iraqi permission to conduct operations, but their troops retain a unilateral right to "legitimate self-defence".