Iraq on Tuesday grounded and inspected a second Iranian aircraft bound for Syria in as many days, but found only humanitarian materiel, Prime Minister Nuri al-Maliki's office said.
The back-to-back searches come after Baghdad said last month it would step up such inspections, 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.
"Iraqi authorities inspected an Iranian cargo plane operated by the company Mahan Air, but only found humanitarian goods," Maliki's spokesman Ali al-Mussawi told AFP.
On Monday, a flight operated by the same private Iranian airline was stopped and searched, with inspectors finding only medical supplies.
Iran branded the inspection as "unacceptable," saying it had protested to Baghdad following the first search.
Its foreign ministry spokesman, Ramin Mehmanparast, said the move was in line with "an Iranophobia project sponsored by the United States, Western countries and the Zionist (Israeli) regime and certain regional countries.
"The searching of the cargo once again showed that these accusations are unfounded," he added.
In a comment piece published in the Washington Post on Tuesday, marking the 10th anniversary of the fall of Baghdad, Maliki wrote that Iraq did not foresee any scenarios in which a military victory ended the Syria conflict.
So, he said, "we oppose all transfers of weapons, to both the government and the opposition, and we are working to ensure that our airspace and territory are not used for such transfers."
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.