The US vice-president has marked American Independence Day in Baghdad, urging Iraqi leaders to do more to encourage political reconciliation, BBC reported.
President Barack Obama has charged Joe Biden with overseeing the American departure from Iraq.
Earlier this week, US forces completed their withdrawal from Iraqi towns and cities, in preparation for a full departure by 2011.
But the move has coincided with an increase in violence.
The vice president ended his three-day visit with a ceremony, conferring US citizenship on 237 men and women who have worked alongside the Americans in Iraq.
They took the pledge of allegiance in one of Saddam Hussein's old palaces.
Most were of Mexican or Filipino origin. But some were Iraqis, and that irony that was not lost on Joe Biden, who remarked that the former Iraqi dictator would be "turning in his grave".
But Mr Biden's visit was also an attempt to foster reconciliation between the various ethnic and religious groups in Iraq, in preparation for the full-scale departure of American troops by 2011.
And for those searching for symbolism, there was perhaps some to be found in the fact that a dust storm prevented a planned trip by the vice president to the autonomous Kurdish region in the north of the country.
Just as the Americans have completed phase one of their withdrawal, reducing their visibility on the streets of Iraq's towns and cities, it is here that tensions have spilled over into the worst violence in recent months.