Iraq said on Monday it has detained a top leader of the Islamic State group and a longtime al Qaida operative in a cross-border operation.

Iraqi Prime Minister Mustafa al-Kadhimi tweeted the news, identifying the man as Sami Jassem, who oversees the IS group’s financial operations and served as the deputy leader of IS under the late Abu Bakr al-Baghdadi.

He described it as “one of the most difficult” cross border intelligence operations ever conducted by Iraqi forces.

Iraqi intelligence officials said that Jassem was detained in an identified foreign country and transported to Iraq few days ago. They spoke on condition of anonymity because they were not authorised to speak of the operation on the record.

Jassem worked with al Qaida in Iraq leader Abu Musab al-Zarqawi, a Jordanian militant who was killed in a US airstrike in Iraq in 2006. He assumed various security positions in Iraq, and moved to Syria in 2015, after the Islamic State group, an al-Qaida offshoot, declared its caliphate in 2014 and became the deputy of Abu Bakr al-Baghdadi, the extremist group's leader.

Al-Baghdadi was killed in a U.S.-led raid in northwestern Syria in 2019.