Iran's Revolutionary Guard says a U.S. drone strike has killed two of its advisers in Iraq, though the U.S. says it has only struck militants in its campaign.

The claim comes as negotiators on Monday attempted to reach a deal on Iran's contested nuclear program.

The Guard said on its sepahnews.ir website the strike happened March 23, just after the U.S.-led coalition began airstrikes to support Iraqi forces trying to retake the Islamic State-held city of Tikrit. It identified the dead as Ali Yazdani and Hadi Jafari, saying they were buried Sunday. It called them advisers.

Reached by The Associated Press, the U.S. Embassy in Baghdad said: "The international coalition is aimed at Daesh only," using an alternate Arabic acronym for the Islamic State group.