Condoleezza Rice and Donald Rumsfeld arrived seperately, but Rice said that the overlapping visits on Wednesday were aimed at avoiding differences between US military and civilian policy-making in Iraq.
"This is a good time for us to go out and to have joint efforts, joint briefings, joint discussions with our people, so we can make certain that those political, military links are strong," the secretary of state said.
The visit comes under a week after Shia politician Jawad al-Maliki was chosen as prime minister and a day after a first reported video appearance by Abu Musab al-Zarqawi, al-Qaeda's frontman in Iraq.
"The answer to the Zarqawi video is not anything that the United States can say, it's what the Iraqis are saying in having formed a government of national unity, despite all the threats and all of the violence," Rice said.
The United States has urged al-Maliki, nominated as prime minister on Friday by Iraq's ruling Shia Alliance, to get a new cabinet in place as soon as possible.
Condoleezza Rice said Iraq was at
a turning point
Elections were held in December, but leaders agreed only last week to form a new coalition government after four months of political wrangling and sectarian violence.
Rumsfeld's trip to Iraq comes as US military commanders contemplate reducing the number of American troops in the country in the coming months.
There are about 132,000 American troops in Iraq.
General George Casey, the US Army commander in Iraq, briefed Rumsfeld on troop requirements.
Rumsfeld indicated earlier this week that the Pentagon intended to reduce the size of the US military presence, but gave no specific numbers or a timetable.
Casey said he was still on his "general timeline" for recommending further reductions in the US force.
Casey, who predicted last year that he would be able to recommend "fairly substantial" troop reductions this year, said the nomination of al-Maliki to form a new government was a step forward.
"We are seeing the situation a little clearer I'd say, and the clearer I see it is, the better I can make my recommendations," he told reporters after meeting Rumsfeld.
Opinion polls show that support for the three-year-old Iraq war is decreasing in the United States.
Rumsfeld has been criticised by six retired generals who have demanded his dismissal, accusing him of disregarding military advice, ruling by intimidation and making strategic errors.