The US troop strength in Iraq is 56,000, a senior Obama administration official said on Wednesday evening, correcting his earlier statement the troop level was down to the 50,000 level Washington has targeted for the end of the month.

"I had incorrect information," the official said.   

NBC News reported earlier on Wednesday night that the last US combat troops had left Iraq. An NBC reporter traveling with the 4th Stryker Brigade drove through the night and arrived in Kuwait just before 4 am local time on Thursday, with TV footage showing the convoy rolling through the border gates and the gate shutting as the last vehicle passed through.

That report set off a flurry of media interest in the drawdown, which will be a milestone in the seven-year war launched under Republican President George W Bush.

But it appeared that even if a combat brigade was on its way out of the country, it did not mean the US combat mission was ending ahead of target.

The Obama administration has said it expects to draw down troop levels to 50,000 by August 31, ending the combat mission and leaving those who remain to train Iraqi armed forces and police units.

Meeting that deadline will mean President Barack Obama is on target to keep his assurances to Americans that all US forces will be out of Iraq by the end of 2011, even as he struggles with a difficult conflict in Afghanistan. Obama faces a war-weary US public as his fellow Democrats seek to hold on to their control of the US Congress in elections in November.   

Bush launched  the US-led invasion in 2003 that ousted Iraqi dictator Saddam Hussein. But the war became unpopular among Americans as US deaths mounted. As of Wednesday, the Defense Department said there were 4,419 US military deaths since the invasion.   

While violence has dipped sharply since the height of sectarian warfare from 2006-2007, Iraq is still extremely fragile and its leaders have not resolved a number of politically explosive issues that could easily trigger renewed fighting.   

Obama has said not a single US service member will remain in Iraq come January 1, 2012, and with opinion polls showing Americans tired of nearly a decade of war in Afghanistan and Iraq, any decision to extend US military involvement in Iraq would be enormously risky for Obama, who is up for re-election in 2012.

He would almost certainly face a backlash from Democrats in Congress and from the left wing of his party, which is already disenchanted with him. The war in Iraq has gone on longer than the US Civil War, World War One and World War Two. - Reuters