An airstrike killed a senior Islamic State leader believed to be the head of the group in Iraq and Syria on Friday, in a joint Iraqi and U.S. operation using intelligence from both countries, Iraq’s rime minister said.

A senior U.S. military official, speaking on condition of anonymity to discuss operational matters, confirmed the strike and said that special operations forces from both countries were in Anbar Province, in Iraq, gathering material from the strike site.

The Islamic State leader, Abdallah Makki Muslih al-Rufay’i, who was also known as Abu Khadija, was “one of the most dangerous terrorists in the world,” the Iraqi prime minister, Mohammed Shia al-Sudani, said in a statement.

Iraqi forces have conducted an aggressive antiterrorism campaign over the last two years, disrupting, killing and detaining a number of the Islamic State cells operating in the country with backing from the United States.

The killing of a senior Islamic State leader in the Middle East comes as the group has been reconstituting in Syria, carrying out more attacks than at any time since it lost control of its territory nearly six years ago. There were more than 300 attacks in Syria alone in 2024, according to the United Nations.

Mr. Al-Rufay’i was thought to be one of the senior leaders in the Islamic State in the region and was believed to hold multiple jobs, according to the most recent report by the United Nations, including helping coordinate among fighters in Iraq, Syria, Turkey and elsewhere.

He is the third leader of the Islamic State in Iraq and Syria to be killed since 2019. In the past, new leaders have been appointed relatively quickly, although their identities may not be widely known for some time.

Since 2019, when the Islamic State was defeated in Iraq and Syria, where it once controlled nearly a third of the geographic area of both countries, it has reconstituted itself and its organization has changed. While it was already expanding into new countries before it lost its territory, the other branches were secondary to its center in Iraq and Syria.

Now, with affiliates in more than a dozen countries across three continents, the organization has evolved, according to Aaron Zelin, a senior fellow at the Washington Institute, who has studied the Islamic State for many years. Some activities, such as media, are controlled in a more central way, while others are left to its branches.

The most deadly attacks in 2024 — in Russia and Iran — were carried out by Islamic State operatives believed to have been working with the affiliate known as IS-Khorasan, which is based in Afghanistan, according to the United Nations.

Eric Schmitt in Washington contributed reporting.