John Kerry in Baghdad on surprise visit: AFP

US Secretary of State John Kerry landed in Baghdad on Sunday on an unannounced visit to press Iraqi leaders for greater cooperation over the conflict in Syria, an AFP reporter with him said.

Kerry's trip, his first to Baghdad since taking office, will also focus on concerns in Washington over months of protests in Iraq's Sunni Arab provinces potentially giving militant groups including Al-Qaeda room to manoeuvre.

It comes just days after the 10th anniversary of the US-led invasion of Iraq that ousted Saddam Hussein and sought to establish a stable democratic ally in the heart of the Middle East, but has instead left a country still grappling with deadly violence and endless political disputes.

Kerry will meet Prime Minister Nuri al-Maliki and parliament speaker Osama al-Nujaifi and press Iraqi officials for greater cooperation on isolating the regime of embattled Syrian President Bashar al-Assad.

Washington has accused Baghdad in particular of turning a blind eye as Iran sends military equipment through Iraqi airspace, flights which Tehran insists transport only humanitarian supplies.