Iraq grounded and searched an Iranian plane bound for Syria through its airspace on Monday, with inspectors finding only first aid and medical equipment, a top official said.

The inspection was the first since Baghdad said last month it would step up such searches, after US Secretary of State John Kerry publicly accused Iraq of turning a blind eye to Iranian flights which Washington says carry military equipment for the Damascus regime.

"We ordered an Iranian cargo plane belonging to Mahan Air to land," Nasser Bandar, the head of Iraq's civil aviation authority, told AFP, referring to one of Iran's two main private airlines.

"The plane responded to the order and landed at Baghdad airport. It was inspected, we did not find any banned material, it was carrying only medical and first aid equipment."

On March 30, Iraq said it would increase its searches of such flights, apparently in response to US pressure.

For months, Washington has accused Baghdad of looking the other way as Tehran sends military equipment through Iraqi airspace, and it has called on Iraqi authorities to make random, unannounced inspections.

Iran insists the planes carry only humanitarian goods.

Iraq previously announced two inspections of aircraft, both in October. But the New York Times reported that Iran appeared to have been tipped off by Iraqi officials as to when searches would be conducted, helping Tehran avoid detection.

Iran has remained a steadfast ally of Syrian President Bashar al-Assad's regime despite the conflict in his country that the United Nations says has killed more than 70,000 people since it erupted in March 2011.