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Iraqi Shiite militia fighters hold the Islamic State flag as they celebrate after breaking the siege of Amerli by Islamic State militants, September 1, 2014. Picture taken on September 1, 2014. reuters/Youssef Boudlal

Three senior members of the Islamic State, including an aide to its leader Abu Bakr al-Baghdadi, were killed in American airstrikes in Iraq, the Iraqi Defense Ministry said Thursday, according to media reports.

Abu Hajar al-Sufi -- believed to be a member of Baghdadi’s inner circle -- was reportedly killed in U.S. airstrikes on the Islamic State stronghold of Tal Afar in Mosul in northwestern Iraq. Two other senior members of Islamic State -- an explosives expert and the military leader of Tal Afar -- were also reportedly killed in the airstrikes.

Although Pentagon spokesman Col. Steve Warren told NBC that he could not confirm the deaths, he added that if the Islamic State leaders were embedded "inside troop formations they are likely to be killed.”

A senior Iraqi security official confirmed the news of the airstrike to NBC and said that it was the most significant blow to Islamic State, formerly known as ISIS, since the start of the U.S. aerial offensive in August.

It is not immediately clear what impact the death of its three senior members would have on Islamic State, as the Sunni extremist group’s organizational structure is shrouded in mystery, but the loss of Baghdadi’s right-hand man cannot be underestimated, an Al Arabiya report said.

Islamic State, which broke off from al-Qaeda in February 2014, has captured vast swathes of land in northeastern Syria and northwestern Iraq.

Baghdadi, who rose to prominence during a Sunni extremist movement following the U.S.-led invasion of Iraq in 2003, had, in June, declared himself the caliph of an Islamic State in the territories his organization has seized.

The news of the successful airstrikes in Iraq came on the day U.S. President Barack Obama and British Prime Minister David Cameron said, in a joint op-ed in The Times of London, that they are looking to build an “international coalition” and strengthen the NATO alliance to intensify military actions against Islamic State.