A report in a prominent U.S. newspaper says the air corridor over Iraq has become a main supply route for weapons for the beleaguered government of Syrian President Bashar al-Assad.

The New York Times, in a story posted on its website late Saturday, said the American effort to stem the flow of Iranian arms to Syria has faltered because of Iraq's reluctance to inspect aircraft carrying the weapons through its airspace. The newspaper says the weapons include rockets, antitank missiles, rocket-propelled grenades and mortars.

The report, which cites anonymous U.S. officials, says the Obama administration is disappointed that American efforts to persuade the Iraqis to randomly inspect the flights have been “largely unsuccessful.”

The New York Times says adding to American frustrations are U.S. intelligence reports indicating Iraqi officials have “tipped off” Iran about the timing of inspections, helping Tehran to avoid detection.

A U.S. official told the newspaper Iraq should be “diligent and consistent” in fulfilling its international obligations by requiring flights over Iraqi territory en route to Syria from Iran to land for inspection, or by denying overflight requests for Iranian aircraft going to Syria.

According to the newspaper account, Iraqi officials continue to insist they oppose the ferrying of arms through Iraq's airspace. The story says Iraqi officials claim Iran is “merely delivering humanitarian aid.” The newspaper reports Iraqi officials say the American charges are “unfounded.”

The New York Times cites an anonymous Iraqi official who said some officials in Baghdad had done the “bare minimum” to placate the U.S. because they are “in fact sympathetic to the Iranian efforts in Syria.”