Iraqis look at profiles of Islamic State members provided by Iraqi authorities in February. (Ahmad al-Rubaye/AFP/Getty Images)

Iraq has arrested five senior members of the Islamic State, including a top aide to the militant group’s leader, Abu Bakr al-Baghdadi, in an operation that involved U.S. and Turkish intelligence support, authorities here said.

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.

“This is the operation that broke the skull of the Islamic State. Other operations were just breaking bones,” said Hashimi, who is regularly briefed by Iraqi intelligence officials. “Soon, Baghdadi will be killed or captured.”

Iraqi and U.S. officials have long said that they believe Baghdadi is hiding in the last area in Syria that the Islamic State controls, close to the border with Iraq.

A spokesman for Iraqi Prime Minister Haider al-Abadi said Thursday that the information gleaned from Ithawi had led to two recent Iraqi airstrikes on Islamic State targets in Syria.

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

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.

The arrests were announced on Iraqi state television late Wednesday and later detailed by the New York Times.

Early Thursday, President Trump touted the detentions in a tweet, saying: “Five Most Wanted leaders of ISIS just captured!”

The spokesman for the anti-Islamic State coalition, Army Col. Ryan Dillon, said in a Twitter post that the arrests were a “significant blow” to the group and underscore the level of cooperation between two U.S. allies in the fight against the Islamic State: the Iraqi security forces and the Syrian Democratic Forces (SDF).

The breakthrough came in February, according to Hashimi, when Turkish officers arrested Ithawi in Turkey using information provided by Iraqi intelligence. He was then extradited to Iraq, where he faced interrogation by Iraqis and Americans.

Over months of questioning, Ithawi provided the banking information and revealed the coded communications the group uses on the messaging app Telegram. Hashimi said that in late April, investigators persuaded Ithawi to contact key members of the Islamic State in Syria and lure them across the border to Iraq, where they were arrested.

They included Syrian Saddam al-Jamal, the head of the Islamic State’s territory in the Syrian province of Deir al-Zour. The three others, a Syrian and two Iraqis, were senior field commanders.

Their pictures were broadcast Thursday on Iraqi state television.

Abadi declared complete victory over the Islamic State in December, after a bloody three-year military campaign to wrest back the cities and towns the group had taken over in 2014. He and American officials have repeatedly said that while major combat is over, the fight against the Islamic State will shift toward intelligence gathering and policing to prevent the group from staging attacks in Iraq.

In Syria, the Islamic State still controls a sliver of territory near the border with Iraq. An American-backed effort to evict the group has been ongoing there, led by the SDF.