A top aide to Islamic State chief Abu Bakr al-Baghdadi is among five senior members of the jihadi group captured in a sting operation by Iraqi authorities backed by the U.S. and Turkey.

“The noose is tightening around” ISIS leader Baghdadi, Iraqi security adviser Hisham al-Hashimi told Reuters on Thursday, a day after Iraqi authorities announced the arrests.

Alluding to Baghdadi’s captured aide, Hashimi indicated to the Washington Post: “One of the men, Ismail al-Ithawi, who goes by the alias Abu Zaid al-Iraqi, is considered part of Baghdadi’s inner circle and has responsibilities for financial, religious and security portfolios across the group’s territory in Iraq and Syria.”

“This is the operation that broke the skull of the Islamic State. Other operations were just breaking bones,” Hashimi added. “Soon, Baghdadi will be killed or captured.”

Iraqi and U.S. officials have long asserted their belief that Baghdadi is hiding in the sliver of territory ISIS controls in Syria, close to the border with Iraq.

U.S. President Donald Trump lauded the capture, describing the detainees as “five most wanted” ISIS terrorists.

The Post reports:

The capture of the men, two Syrians and three Iraqis, represents a breakthrough in the hunt for Baghdadi, experts said Thursday and underscores the deep security cooperation within the American-led coalition against the Islamic State despite political tensions roiling the region.

One of the men, Ismail al-Ithawi, who goes by the alias Abu Zaid al-Iraqi, is considered part of Baghdadi’s inner circle and has responsibilities for financial, religious and security portfolios across the group’s territory in Iraq and Syria, said Hisham al-Hashimi, an expert on the Islamic State who advises the Iraqi government.

Saad al-Hadithi, a spokesman for Iraqi Prime Minister Haider al-Abadi, reportedly said Thursday that Ithawi provided information that led to two recent Iraqi airstrikes on ISIS targets in Syria.

“This is a demonstration of how Iraq’s intelligence capability has developed,” said the spokesman, Saad al-Hadithi.

Reuters learned that authorities used Ithawi’s phone to capture the other four ISIS commanders, reporting:

Iraqi agents are holding a top aide to Islamic State leader Abu Bakr al-Baghdadi and used an app on his mobile phone to lure four commanders from the group into a trap, a security advisor to the Iraqi government said on Thursday.

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Iraqi agents used the Telegram messaging app on Eithawi’s mobile phone to lure other Islamic State commanders to cross the border from Syria into Iraq, where they were captured, Hashimi said.

Authorities also gleaned information from Baghdadi’s aide that has helped deliver a blow to ISIS’s finances.

“Hashimi said Ithawi also provided banking information to Iraqi and American interrogators that has helped cut off valuable sources of funding for the Islamic State, which is also known as ISIS,” reports the Washington Post.

The arrest of the senior ISIS members dealt a “significant blow” to the group, U.S. Col. Ryan Dillon, the spokesman for the American-led coalition against the terrorist group, declared.

While U.S.-led coalition forces and their local allies have decimated ISIS in Iraq, the group still controls a sliver of territory in Syria.

The U.S. military has repeatedly warned that ISIS remains a threat.