US Defence Secretary Robert Gates has arrived in Iraq on a previously unannounced visit.
Mr Gates' visit comes amid continuing violence in Baghdad
Mr Gates flew to Baghdad from Israel, where he told reporters he wanted to see "faster progress" towards political reconciliation in Iraq.
His visit came a day after bombings in Baghdad killed nearly 200 people. At least 11 people died in another blast in the capital on Thursday.
The violence was the worst since a US-led security push began in February.
Shortly after arriving, Mr Gates went by helicopter to the insurgent stronghold of Falluja, where he met Gen David Petraeus, the commander of US forces in Iraq, and Gen Peter Pace, chairman of the Joint Chiefs of Staff.
The visit is Mr Gates' third to Iraq since he took office in December.
As he set off for Baghdad, the defence secretary said the Iraqi leadership must be aware that the US' military commitment to the country was not "open-ended".
Some 28,000 extra US troops were ordered to Iraq as part of President Bush's security offensive in Baghdad.
'Soldiers of Satan'
Mr Gates' arrival in Baghdad was preceded by fresh violence in the Iraqi capital.
At least 11 people died when a suicide car bomber rammed a fuel lorry, police said.
Another 21 people were injured in the blast, which happened in the mainly Shia Karrada district of the city at 1315 (0915 GMT).
Separately, the army said 20 insurgents had been killed and 84 arrested in operations across Iraq.
Iraqi Prime Minister Nouri Maliki condemned Wednesday's bombings, describing those behind the attacks as "soldiers of Satan".
He also ordered the arrest of the army commander responsible for security in Sadriya district, where 140 people died in a blast at a food market.
Car and suicide bombings have occurred almost daily in Baghdad in recent months, despite the security crackdown.
The bombers are proving that they can slip through the tightened security net, says the BBC's Jim Muir in Baghdad.