Any declines in Iranian oil exports are normal, though supplies to Asian economies are in line with contractual obligations, an executive said.

Mohsen Qamsari, director of international affairs at the National Iranian Oil Co., said exports to China and India are in line with contractual volumes.

In its latest monthly oil report, the International Energy Agency said Iranian oil exports were down by as much as 36 percent to 510,000 barrels per day. Qamsari said any variances in export levels were natural.

Iran secured some relief from Western sanctions targeting its energy sector in exchange for a November agreement from Tehran to curb nuclear research activity. The U.S. government said Iran can export oil so long as it stayed around 1 million bpd, according to the terms of the November agreement.

Qamsari offered no export level for India. Exports to China, he said, increased 36 percent in May, or around 757,000 bpd, from last year's levels.

Iran says China is its largest oil client.