Syrian Kurdish fighters and American forces have captured a senior member of the Islamic State group, a militant described as one of its "key facilitators," the force said Friday.

Mahmdouh Ibrahim al-Haji, also known as Abu Youssef, was taken into custody on Thursday in the northern Syrian city of Raqqa, according to the U.S.-backed Syrian Democratic Forces, just days after the U.S. military said it had captured another IS operator in northern Syria.

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According to a statement from the Syrian Kurdish fighters, al-Haji "was actively involved in enabling ... terrorist cells in the region." It added that the joint force raided his hideout west of Raqqa, "and successfully apprehended him."

Despite their defeat in Syria in March 2019, IS sleeper cells are still able to carry out deadly attacks that have killed scores of people over the past year.

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The U.S. has approximately 900 troops in Syria focused on countering the remnants of IS, which had held a wide swath of the country until 2019.

IS declared a self-styled caliphate across the territory in Syria and Iraq that it seized in 2014. It was declared defeated in Iraq in 2017, following a three-year battle that left tens of thousands of people dead and cities in ruins.

U.N. experts said last month that IS still commands between 5,000 and 7,000 members across its former stronghold in Syria and Iraq and that its fighters pose the most serious threat in Afghanistan today.