US Secretary of State Condoleezza Rice has praised Iraq's new prime minister, saying he is focused on and committed to forming a national unity government.
Mr Maliki's nomination ends months of wrangling over the role
Ms Rice was speaking after she and Defence Secretary Donald Rumsfeld met the PM, Nouri Maliki, in Baghdad.
"He was really impressive," Ms Rice said after their talks, while Mr Rumsfeld said he was "most encouraged".
Mr Maliki is trying to put together a government after months of deadlock and start the work of curbing Iraqi unrest.
The visit by two of the most senior members of the Bush administration was aimed at encouraging Mr Maliki to push forward with assembling a broad-based coalition.
They held a 50-minute meeting at the US ambassador's residence in the highly fortified Green Zone.
"He understood his role and the role of the new government to really demonstrate that it's a government of national unity in which all Iraqis could trust," Ms Rice said.
"We came expecting to say that the ministries also needed to be ministries of national unity, just like it was government of national unity, only to hear him say it first."
Ms Rice and Mr Rumsfeld's visit comes amid a recent surge in US combat deaths in Iraq.
It also follows the emergence of a video believed to be from the head of al-Qaeda in Iraq, Abu Musab al-Zarqawi, in which he threatened those who might participate in a unity government and its armed forces.
The BBC's Jim Muir in Baghdad says Washington is keen for Mr Maliki to form a government that gives a strong representation to the Sunnis in whose community the insurgency is based, and so win over Sunni public opinion.
Mr Maliki, who comes from the Shia political grouping, the Dawa party, has won praise from Sunni leaders for his pledge to dissolve militias and promote unity.
Both Ms Rice and Mr Rumsfeld said that dismantling the militias would take time.
"Iraqis will have to determine how to do this given their circumstances and their capabilities," Ms Rice said. "How we support them will be part of that discussion."
Speaking at a joint news conference with Mr Rumsfeld, Gen George Casey, the top US military commander in Iraq, said Iraq's selection of new government leaders was a "major step in the process" towards returning US troops home.
Words of encouragement for Iraq's security forces
"I'm still on my general timeline," he said, declining to specify when the first substantial troop withdrawals would begin.
Mr Rumsfeld said he and Gen Casey had also discussed how best to work with Iraq's new leaders on the dividing up of the security of Iraq between domestic and US forces.
He hailed the development of Iraq's own security forces, which he said were making "impressive progress".
The Bush administration is under mounting domestic pressure over Iraq and hopes to start reducing troop levels over the next few months, our correspondent says.
There are currently more than 130,000 US troops in Iraq, so it is vital that Iraqi forces should be in a position to take over and that the new Iraqi government should be solid enough to take the strain, our correspondent says.