BAGHDAD - U.S. Secretary of State John Kerry is in Iraq on an unannounced visit to urge Iraqi leaders to stop Iranian overflights of arms and fighters heading to Syria and to overcome sectarian differences that still threaten Iraqi stability 10 years after the American-led invasion that toppled dictator Saddam Hussein. Kerry flew into Baghdad on Sunday from Amman after accompanying President Barack Obama to Israel, the Palestinian Authority and Jordan. The official, who spoke on condition of anonymity because she was not authorized to publicly preview Kerry's meetings, said there are clear links between al-Qaida linked extremists operating in Syria and militants who are carrying out terrorist attacks in Iraqi territory with increasing regularity. Kerry will tell al-Maliki that Iraq cannot be part of the political discussion about Syria's future until it clamps down on the shipments, the official said. 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. His arrival came just three days after the anniversary of the U.S.-led war that began on March 20 with an airstrike on Dora Farms in southern Baghdad in a failed attempt to kill Saddam Hussein. The invasion and toppling of Hussein sparked years of bloodshed as Sunni and Shiite militants battled U.S. forces and each other, leaving nearly 4,500 U.S. soldiers and more than 100,000 Iraqis dead. Violence has ebbed sharply since the peak of Sunni-Shiite fighting that pushed the country to the brink of civil war in 2006 and 2007. But insurgents are still able to stage high-profile attacks, and sectarian and ethnic rivalries remain threats to the country's long-term stability. Earlier this week, an al-Qaida in Iraq front group claimed responsibility nearly 20 attacks that killed 65 people across the country on Tuesday and Wednesday. The Islamic State of Iraq said it unleashed the car bombs and other explosions to avenge the executions and "massacres" of convicted Sunni inmates held in Iraqi prisons. Its claim came on the 10th anniversary of the start of the war, although it made no reference to the significance of the date.