US Secretary of State John Kerry has arrived in Iraq for an unannounced visit to urge leaders to overcome sectarian differences that still threaten the country's stability following the 10-year anniversary of the US-led invasion that toppled dictator Saddam Hussein.
Mr Kerry flew into Baghdad from Amman on Saturday after accompanying President Barack Obama to Israel and Jordan.
Officials travelling with him said he would press Iraqi Prime Minister Nouri al-Maliki and other senior officials on democratic reforms and urge them to stop overflights of Iranian aircraft carrying military personnel and equipment to support the Syrian government as it battles rebels.
The flights have been a source of contention between the US and Iraq and Mr Kerry will tell the Iraqis that letting them continue will threaten the country's stability.
A senior US official said the sheer number of overflights, which occur "close to daily," as well as overland shipments to Syria through Iraq from Iran, was inconsistent with Iranian claims that they are only carrying humanitarian supplies.
The official said it was in Iraq's interest to prevent the situation in Syria from deteriorating further, particularly as there are fears that Iranian-backed extremists may gain a foothold in the country. The official said there are links between al Qaida-linked extremists operating in Syria and militants carrying out terrorist attacks in Iraqi territory.
Mr Kerry will tell Mr al-Maliki that Iraq cannot be part of the political discussion about Syria's future until it clamps down on the shipments.
As Iraq approaches provincial elections next month, Mr Kerry will also stress the importance of ensuring that all elements of society feel enfranchised, the official said. A recent decision to delay the polls in Anbar and Nineveh provinces is a "serious setback" to Iraq's democratic institutions and should be revisited, the official said.
Mr Kerry also plans to speak by phone with Massoud Barzani, the head of the Kurdish Regional Government based in Irbil to encourage the Kurds not go ahead with unilateral actions - especially involving oil, like a pipeline deal with Turkey. He will not meet with Iraqi Foreign Minister Hoshyar Zebari because he is in Doha for an Arab League meeting.
He will stress the "importance of maintaining the unity of Iraq," say that "separate efforts undercut the unity of the country" and that "the Kurdish republic cannot survive financially without the support of Baghdad," the official said.