US Secretary of State Condoleezza Rice has held talks with leaders in the Kurdish area of northern Iraq.
Condoleezza Rice urged Kurds to share oil revenues
During her visit - the latest leg of a regional tour - Ms Rice met Kurdish regional leader Massoud Barzani.
They discussed the oil sector, which Kurds see as crucial to their future.
They believe their region has huge untapped reserves, and they want to expand to include the oil-rich Kirkuk province - which is also claimed by Iraq's Arabs and Turcomans.
Ms Rice urged the Kurdish leader to work with Sunni and Shia groups, particularly on the issue of sharing Iraq's oil wealth across
the country .
She flew into Baghdad on Thursday for an unannounced visit and held talks with Prime Minister Nouri Maliki.
The Kurds have been signing oil exploration deals with foreign companies, stirring unease in Baghdad.
Ms Rice has been seeking reassurances that the Kurds remain committed to autonomy within a unified, federal Iraq.
After leaving Baghdad, she travelled to the mountain retreat of the Kurdish leader, who in recent weeks raised concerns by banning the display of the Iraqi flag in government buildings.
Kurdish autonomy in northern Iraq is set out in the federal system adopted by the new Iraqi constitution.
But there are tensions over how it will work, with Sunnis concerned that Kurds in the north and the Shias in the south may split off, taking most of the country's oil resources with them, says the BBC's Jim Muir in Baghdad.
Ms Rice and Mr Barzani met for 45 minutes and later held a joint press conference, in which Mr Barzani described the talks as constructive.
He told journalists that Iraqi Kurds had "the right to self-determination", but said he was committed to a "federal democratic and pluralistic Iraq", the Associated Press news agency reported.
He also said he was "for a fair distribution of oil revenues for the Iraqis", the French news agency AFP said.
In Baghdad on Thursday, Ms Rice said that oil had to be a resource for the Iraqi people as a whole, "not one that would help to make the country less unified".
She warned Iraqi leaders they must act quickly to settle their differences to help tackle soaring sectarian violence.
Kurdish independence, especially if it meant taking control of the northern oil, is something the Americans would not support, our correspondent says.
Ms Rice visited Iraq during a tour of the Middle East that has included talks with Israeli and Palestinian leaders, as well as stops in Cairo and Saudi Arabia.