US Secretary of State Condoleezza Rice has flown to Baghdad as she continues a previously unannounced visit to Iraq.
In her eighth visit as secretary of state, Ms Rice was expected to pressure Prime Minister Nuri al-Maliki's Shia-led government to break the political deadlock and reach an accommodation with minority Sunni Arabs and Kurds.
The government has been paralysed by deep divisions and mistrust between leaders of Iraq's different religious sects and ethnic groups. It has made little headway in passing laws seen as vital to reconciliation.
As a helicopter carrying the Secretary of State and her entourage landed in Baghdad's Green Zone, a car bomb exploded just on the other side of the Tigris river, killing four people and injuring seven.
Ms Rice met a group of Iraqi political leaders at President Jalal Talabani's residence and was planning to meet the Prime Minister later.
The US Secretary of State earlier visited the northern city of Kirkuk, where she met members of the local provincial council.
A clause in Iraq's constitution provides for a referendum to be held there by the end of this year to determine whether the area joins Kurdistan, but it has been delayed because of the deep divisions among Arabs and Kurds.
The president of the Kurdish region has refused to meet Ms Rice because of the US position on Turkey sending soldiers into northern Iraq.
Further north, Turkish troops entered Iraq early today in a further operation designed to combat separatist Kurdish rebels.
300 Turkish troops crossed into Kurdish territory overnight and moved 2-3 km deeper into Iraq this morning.
The troops are said to be lightly armed as they moved into the Gali Rash area, a mountainous district near the border.
Turkey says it has a right to use military force to combat Kurdish separatist rebels based in northern Iraq.
Jabbar Yawar, spokesman for the Kurdish Peshmerga security force, said the area they entered was a deserted area and there was no Iraqi force or peshmerga presence there.
