Turkish intelligence helped Iraq capture a senior Daesh terrorist leader who had been hiding out in northwestern Syria, three security sources said Tuesday, in an operation that points to closer cooperation against remnants of the terrorist group.

Iraq announced Monday that its security forces had captured Sami Jasim, an Iraqi national, in what it described as "a special operation outside the borders." It did not give details on when or where he was seized.

Jasim is one of the most senior Daesh leaders to be taken alive. He was a deputy to Daesh's founder Abu Bakr al-Baghdadi, killed during a U.S. raid in 2019 in Syria's northwest, and a close aide to its current leader Abu Ibrahim al-Hashemi al-Quraishi, the Iraqi government said.

Turkish intelligence had also played a key role in the death of al-Baghdadi by detaining and extraditing one of his aides to Iraq, who provided U.S. authorities with critical information for locating the vicious man.

Turkey also captured the wife of al-Baghdadi in Syria, and his older sister in northwestern Syria, calling the arrest an intelligence "gold mine."

Most recently, al-Baghdadi's right-hand man, an Afghan national code-named "Basim" has been captured in Istanbul in a joint operation by Turkish intelligence and police earlier this year.

A senior regional security source and two Iraqi security sources told Reuters that Jasim had been in northwestern Syria and that Turkish intelligence had been key to his capture. The sources spoke on the condition of anonymity because they were discussing covert operations.

Officials in the Iraqi and Turkish governments declined to comment on the sources' accounts of Jasim's capture.

Closer cooperation between Iraq, from where many Daesh leaders came, and Turkey, which has influence in northern Syria, could help tighten the noose on remnants of the terrorist group, even after the U.S. military has reduced its presence in the region.

Northwestern Syria is the last major bastion of insurgents who have been fighting Damascus. Turkey holds big sway in the area having sent in troops in a series of operations beginning in 2016 and also backs some of the opposition groups there who are fighting Bashar Assad's forces.

The senior regional security source said Jasim was in northwestern Syria when he was caught with help from local security forces. The two Iraqi sources said he was detained in Turkey shortly after being lured over the border.

One of the Iraqi sources said Iraqi intelligence agents had been tracking Jasim for months. Information from a Daesh prisoner detained last year had contributed to his capture, the second Iraqi security source said.

The sources declined to give further details including when Jasim was captured, saying this would risk future operations.

His capture could yield significant intelligence about the remnants of the Daesh terrorist group which was driven from its cross-border "caliphate" in Syria and Iraq years ago but still carries out attacks in both countries.

Jasim had been flown to Iraq from Turkey in a military plane, the two Iraqi security sources and an Iraqi military source close to the Iraqi military aviation service said.

One of the Iraqi sources shared a photo they said showed Jasim being brought to Iraq on a plane. It showed a person in a yellow jumpsuit, their face covered, being escorted from the plane by Iraqi security personnel in balaclavas. Reuters could not independently verify the authenticity of the image.

Asked by Reuters on Monday about Jasim's capture, the U.S.-led coalition said it would not comment on specific operations but applauded Iraqi forces that "regularly lead and conduct destructive blows to the remnants" of Daesh.

According to the website of the U.S. Department of State's counterterrorism rewards program, Rewards for Justice, Jasim has been "instrumental in managing finances for ISIS's terrorist operations." The United States had offered $5 million for information on Jasim.

"The Iraqis will be trying to ascertain as much as they can about the networks and links he had in Iraq and across borders. They will be very interested in fundraising in particular," said Raffaello Pantucci, a senior associate fellow at the RUSI security think tank.

Daesh's cross-border "caliphate" once spanned a third of Syria and Iraq, inspiring affiliates including one in Afghanistan. But the group was steadily beaten back in Syria and Iraq by local forces helped by the U.S.-led coalition.

Turkish security forces have nabbed at least 850 suspects with links to Daesh in the first three months of 2021, dealing a heavy blow to the terrorist group's presence in the country and its activities in the region.

Being one of the first countries that recognized Daesh as a terrorist group in 2013, Turkey has been frequently conducting domestic and cross-border operations against the group for years in order to eliminate a major global terrorism threat.