Updated

In a curiously timed allegation coming on the eve of a key deadline for nuclear talks, Iran's Revolutionary Guard on Monday claimed a U.S. drone strike killed two of its advisers in Iraq -- an allegation the U.S. disputed.

"We are looking into this, like we do all claims, but we don't think we did it," a spokesman for the U.S.-led coalition based in Kuwait told Fox News, as Pentagon officials pushed back on Iran's claims.

The Guard said on its sepahnews.ir website the strike happened March 23. This would appear to be after the U.S.-led coalition began providing intelligence and surveillance assistance for the Iraqis in their campaign to retake the Islamic State-held city of Tikrit -- but before the U.S., on March 25, began launching airstrikes at the Iraqi government's request.

The Guard identified the dead as Ali Yazdani and Hadi Jafari, saying they were buried Sunday. It called them advisers, without elaborating on whether Iran contacted Iraqi or U.S. forces after the strike.

Officials in the Pentagon would not speculate if the claims made by Iran are linked to the Tuesday deadline over nuclear negotiations in Switzerland between Iran and six other nations including the U.S. Iran reportedly has been making new demands for concessions in the run-up to that deadline.

Iran occasionally reports on the death of its forces in Iraq and Syria, where it is backing embattled President Bashar Assad, but Monday's allegation marks the first time Iran has said it has lost forces in an attack by the U.S. in those campaigns.

The U.S.-led coalition began a campaign of reconnaissance missions around Tikrit, Saddam Hussein's hometown, on March 21 and later launched airstrikes in support of large-scale operations to retake it after Iraqi efforts had stalled.

Reached by The Associated Press about the Guard's claim, 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.

"All airstrikes are carried out at the request of the Iraqi government and in full coordination with the (Iraqi) Ministry of Defense," the embassy said, without directly addressing the Iranian claim.

The Islamic State group now controls a third of both Iraq and neighboring Syria. The U.S. began airstrikes against the group in August, while Iran has offered advisers and other assistance to Iraq to fight the extremists.

The offensive to retake Tikrit largely has been waged by Iraqi troops and Shiite militias advised by Gen. Qassem Soleimani, commander of the Guard's elite Quds Force. Several Shiite militias announced Thursday that they would boycott the Tikrit operations due to U.S. involvement, but Army Gen. Lloyd Austin, head of U.S. Central Command, told a Senate hearing Thursday that the U.S. agreed to Iraqi government requests to support the operation on the condition that the militias wouldn't be involved.

On Friday, Iraqi media outlets reported casualties among Iraqi security forces near the University of Tikrit, allegedly from U.S. airstrikes. But the U.S. Embassy in Baghdad denied those claims, saying "no coalition airstrikes took place during the time or in the vicinity of these alleged casualties."

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.