A Treasury spokesperson said that Turkey shares U.S. interests in maintaining a well supplied oil market, despite a back-up of tankers waiting to transit the Bosphorus Strait at Istanbul.

"We've been in touch with Turkey about how the price cap only applies to Russian oil, and explained that the cap doesn't necessitate additional checks on ships passing through Turkish waters," the spokesperson said in a statement. "Our understanding is that virtually all of the delayed tankers are not carrying oil from Russia and are not affected by the cap."

(Reporting by Andrea Shalal in Fort Worth; writing by David Lawder in Washington)