US Secretary of State John Kerry has made an unannounced visit to Baghdad to urge Iraqi leaders to stop Iranian flights over Iraq carrying arms and fighters for the Syrian regime.

Mr Kerry told Prime Minister Nouri al-Maliki and other senior officials to overcome the sectarian differences that remain a threat to the country’s stability ten years after the invasion of Iraq.

The US believes the aircraft are carrying weapons destined for Syrian President Bashar al-Assad’s supoorters, but Iran and Iraq claim they are transporting humanitarian supplies.

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Mr Kerry asked for the planes to land in Iraq for inspection if a complete ban was not possible.

Former Secretary of State Hillary Clinton secured a pledge from Iraq to inspect the flights last year, but only two aircraft have undergone the checks by Iraqi authorities, US officials said.

The officials claim the number of flights – which are said to occur on an almost daily basis – and the Iranian shipments trucked to Syria via Iraq, were inconsistent with claims they are only carrying humanitarian aid.

A US source told the Associated Press that there are links between al-Qaeda-associated extremists operating in Syria and militants carrying out terrorist attacks in Iraq.

Mr Kerry will warn Mr al-Maliki that Iraq will not be a part of the international discussion on Syria’s future unless it makes a serious effort to stop Iranian shipments.

The Secretary of State’s visit came just days after the anniversary of the start of the Iraq War that toppled dictator Saddam Hussein.