The number of US troops in Iraq has reached its highest ever level - nearly 162,000 - US officials have said.
The troop level is expected to return to normal within a few weeks
But the peak is due to the regular replacement of units and does not represent an additional troop build-up, a US Defence Department spokesman said.
President George W Bush announced in January a surge of 30,000 extra troops, mainly in and around the Iraqi capital, Baghdad, as part of a security drive.
Correspondents say the Pentagon is playing down this particular peak.
The previous highest level came in January 2005, when 161,000 US troops were deployed ahead of Iraq's first national elections since Saddam Hussein was overthrown.
Pentagon spokesman Bryan Whitman said the main reason for the temporary rise in troop numbers was that the US Army's 2nd Stryker Cavalry Regiment had arrived to replace the 2nd Infantry Division's 3rd Stryker Brigade.
Military units typically overlap their tours so the outgoing unit can help its successor acclimatise.
"There is no change to the level of effort and the combat power that we are projecting into Iraq," Mr Whitman told the Los Angeles Times newspaper.
Since the arrival in June of the last additional US forces deployed to Iraq as part of the surge, the number of troops has remained steady at about 157,000.
The level will probably return to normal within a few weeks and then rise again as other brigades are rotated, Mr Whitman said.
The BBC's Nick Childs says that although the Pentagon is playing down the peak, the number of US troops in Iraq has always been hugely controversial.
Early on, critics said the insurgency had taken hold because there were too few troops.
US casualties have increased political pressure on the military
But just when President Bush decided to send more, the political pressure in Washington shifted to become predominantly for withdrawal, or at least for cuts.
Many argue that, even now, the US has deployed far fewer troops than traditional doctrine suggests are needed to fight an insurgency in a country the size of Iraq.
The generals in charge insist that it is not just about numbers, but about a change in tactics as well and that the key battle front right now is the political one.
The US force in Iraq now is more than one-and-a-half times the size of the entire British army and it is straining the US military almost to breaking point, our correspondent says.
However, the force pales in comparison with the one the US had in Vietnam during the war - more than 500,000 troops in all - although that was a very different time and different circumstances, he adds.
The news of the peak comes a day after officials said five US soldiers had been killed in Iraq since Saturday, bringing the total killed since March 2003 to 3,680.
Three of the soldiers were killed by roadside bombs, which the second-highest US commander in Iraq has said are increasingly being supplied by Iran.
Lt Gen Raymond Odierno told the New York Times that "explosively formed penetrators" were used to carry out 99 attacks in July, accounting for a third of US combat deaths.
Gen Odierno said Iran was supplying increased numbers of the devices to Shia militants to step up pressure on the US ahead of a report by his superior to Congress in September.
"Over the last three to four months, it has picked up in terms of equipment, training and dollars," he said.