Gates' arrival was the second public visit by a top US official to Iraq following the withdrawal of US troops from Iraqi cities June 30.

On June 4, US Vice President Joe Biden celebrated US Independence Day with his country's troops in Iraq, presiding over a ceremony to confer citizenship to hundreds of non-US nationals fighting with the US military in Iraq.

Gates, whose last visit to Iraq was in September 2008, is also expected to visit Iraq's Kurdish region and to meet Massoud Barzani, incumbent president of the Kurdistan semi-autonomous region.