Calling it a “joke,” U.S. defense officials today pushed back strongly against the Russian Defense Ministry's claim that a Russian airstrike, not an American one, killed a top ISIS leader in Syria.

Russia’s defense ministry said today in a statement that Abu Muhammad al-Adnani was among roughly 40 ISIS fighters killed when a Russian Su-34 bomber struck a large group of ISIS militants in Maaratat-Um-Haush in northern Aleppo province.

But Russia’s version of events is at odds with the Pentagon's statement Tuesday that al-Adnani had been targeted by a "precision airstrike" near Al-Bab in Aleppo Province.

“The report is not credible,” a U.S. defense official said of the Russian claim of credit.

“It’s a joke” another defense official said bluntly. "It would be funny if not for the character of the campaign the Russians have undertaken in Syria.”



ISIS Claims Top Spokesman Killed in Syria



“We have no information to support Russia's claim that they also carried out a strike against Adnani,” Pentagon Press Secretary Pete Cook said at a briefing today.

"From the start, Russia, as you know, has spent most of its time, its military campaign supporting and propping up the Assad regime," Cook added of Syrian President Bashar Hafez al-Assad.

"It has not devoted much, if any, effort that we're aware of targeting ISIL's leadership. And at the same time, we have not seen the Russian military campaign use precision weaponry on a regular basis as well.”

The United States continues to assess the results of the airstrike through what Cook called “a rigorous process.”

“We're going to follow that process. I know what ISIL itself has said. I know what the Russians have said. We don't trust -- we're not going to be satisfied simply to trust ISIL and the Russians on this when we go through our process.”

He wouldn’t speculate on why Russia would make a claim about an al-Adnani airstrike, but said it could have been “a misunderstanding on their part.”

U.S. officials have often criticized Russia's use of non-precision weapons in Syria that have resulted in civilian casualties.

Al-Adnani was targeted Tuesday in a daylight drone strike as he rode in a vehicle with at least one other ISIS combatant,” according to two U.S. defense officials.

That contradicts the Russian claim that he was killed among a large group of ISIS fighters.

The U.S. officials said the assessment of the results of the drone strike will continue.

ISIS's media arm, the Amaq news agency, first reported al-Adnani's death Tuesday in a social media post, stating he had been killed while inspecting troops in Aleppo.

Al-Adnani was one of the U.S. top targets among ISIS's leadership, overseeing the group’s elaborate propaganda operations and credited with masterminding its strategy of staging terror attacks abroad, including the Nov. 13 Paris attacks and the airport attacks in Brussels and Istanbul.

Al-Adnani’s death would be a coup for both sides fighting to destroy the Islamic State, also known as ISIL. Russian and U.S. aircraft have delivered thousands of strikes against the group, though U.S. bombing has been more focused on its fighters in Iraq.

“Al-Adnani’s removal from the battlefield would be a significant blow to ISIL,” Cook said Monday.

Cook described Adnani as the “principal architect” of ISIS’s external operations.

A Syrian national born Taha Sobhi Falaha, al-Adnani was a core member of ISIS, considered by some as second only to leader Abu Bakir al-Baghdadi.

Al-Adnani shaped the terror group’s use of gruesome propaganda that has become its hallmark, as well as its calls for attacks abroad, including by so-called lone-wolf attackers, according to terrorism experts and U.S. intelligence officials.