Condoleezza Rice arrived in Baghdad on Thursday afternoon and met with Nuri al-Maliki, the Iraqi prime minister, Lou Fintor, US embassy spokesman said.
In the course of her visit, Rice is expected to meet with al-Maliki, the Iraqi prime minister, and Jalal Talabani, the president, as well as Sunni leaders.
In a news conference aboard her plane, Rice said she will tell Iraqi leaders they have limited time to settle the political differences that have spurred sectarian violence.
"They don't have time for endless debate of these issues," Rice said.
"They have really got to move forward. That is one of the messages that I'll take, but it will also be a message of support and what can we do to help."
Rice said Iraqis must solve for themselves complex problems such as the division of oil wealth, possible changes to the national constitution and the desire for greater autonomy in various regions of the country.
"Our role is to support all the parties and indeed to press all the parties to work toward that resolution quickly because obviously the security situation is not one that can be tolerated and it is not one that is being helped by political inaction," she said.
Rice arrival in Baghdad was delayed by 30 minutes because of "indirect fire" at the airport complex, Sean McCormack, the State department spokesman, said.
Her plane circled until it was deemed safe for her to land.
Car bombs, as well as other explosions and shootings, killed 34 people across the country on Wednesday.
At least 21 US soldiers have been killed since Saturday, a disproportionately high number.
Most of the casualties have been in Baghdad amid a massive security sweep by American and Iraqi forces that has been going on since August.
Rice described the task as "the ability to get everybody to understand precisely how their interests are going to be represented and how their interests are going to be served in this political process."