US Secretary of State Colin Powell has met the Iraqi president after arriving in Baghdad on an unannounced visit.
Powell is the most senior US official to visit Iraq since the handover
Mr Powell restated Washington's determination to stand by the Iraqi interim government.
He also promised that the US will speed up the flow of cash for reconstruction to help deal with continuing violence.
The Iraqi President, Ghazi al-Yawer, said they had not discussed the latest Saudi Arabian plan to form an international Muslim force for Iraq.
He also said he regretted the delay in holding a national conference that was due to select an interim assembly beginning on Saturday.
The conference is now expected to be held in mid-August. Its postponement follows a surge in violence in recent days.
The BBC's Jill McGivering who is accompanying Mr Powell says the visit is being seen in Baghdad as a gesture of support for an interim government facing continuing violence.
Following his meeting with President Yawer, Mr Powell said he had sent the clear message that the rate of spending on reconstruction projects would be increased sharply, employing people who wanted jobs.
"The rate of commitment, the rate of expenditure will be increasing markedly in the immediate future and this will affect the security situation," he said.
He also had a warning for Iraq's neighbour Iran, saying the US was uneasy about attempts by Iran to gain influence in southern Iraq and was monitoring its actions closely.
Violence has surged this week in Iraq
Mr Powell went on to meet US military commanders and diplomats in the Iraqi capital.
The AFP news agency reported four explosions in central Baghdad on Friday.
The US military has not identified the source of the explosions.
Mr Powell arrived as US troops continued operations in the flashpoint city of Falluja, which the US says has become a safe haven for militants since an Iraqi force was put in control in April.
Reports from the city, quoting hospital sources and police, say at least nine Iraqis were killed and more than a dozen wounded in clashes overnight between US soldiers and insurgents.
A doctor at the city's general hospital told Reuters news agency that some of the injured were in a serious condition after the fighting.
Mr Powell's visit was kept a closely guarded secret right until the last minute.
On Thursday, Mr Powell met Iraqi Prime Minister Iyad Allawi in Saudi Arabia, where both gave a cautious welcome to a Saudi proposal to send Arab or Muslim forces to Iraq.
Foreign ministers from Algeria, Bahrain and Tunisia on Thursday discussed the possibility of sending troops to Iraq.
The talks in Tunis were attended by Iraqi Foreign Minister, Hoshyar Zebari, and the Arab League Secretary General Amr Moussa.
Islamic militants have threatened to retaliate against any country which contributes to the force.