President Obama has authorized the Pentagon for the first time to target and kill individual leaders of Islamic State in Iraq and Syria, a key component of his plan to go on the offense against the Sunni extremist group, according to U.S. military officials.

At the top of the list is Abu Bakr al-Baghdadi, the movement’s self-declared leader, according to two U.S. military officials who spoke on condition of anonymity to discuss operations.

Baghdadi has rarely appeared in public even as his group has raised its global profile by rapidly seizing territory across Syria and Iraq. The Islamic State released a video two months ago that showed him preaching in a mosque in the northern Iraqi city of Mosul; it was the first time he has appeared in a propaganda production.

Prior to this week, Obama had imposed restrictions that prevented the U.S. military from targeting Islamic State leaders even if it knew their whereabouts. U.S. forces could only launch airstrikes against the group to protect U.S. personnel or property in Iraq, to protect refugees or to secure key installations, such as two large dams on the Tigris and Euphrates rivers that Islamic State has tried to capture.

Rear Adm. John Kirby, a Pentagon spokesman, declined to comment Thursday about Obama’s directive but acknowledged that there would be a shift in military operations.

“One of the ways you get at, and you destroy the capabilities of an enemy like [Islamic State] is to be pretty aggressive against them,” he said. “And that does include disrupting their ability to command and control and to lead their own forces.”

On Wednesday, Obama said he had ordered 475 more U.S. troops to Iraq, bringing the total there to about 1,600. The new troops will arrive in Iraq “over the next week or so,” Kirby said.

Among them is a detachment of about 125 personnel who will fly armed U.S. surveillance aircraft from inside Iraq for the first time since Obama authorized the start of the air campaign against Islamic State last month. The aircraft will be based in northern Iraq in the city of Irbil. U.S. officials are still determining which types of planes will be sent, but the detachment will not include drones, Kirby said.

The U.S. military has carried out more than 150 airstrikes in Iraq since last month. About two-thirds have been launched by drones and fighter airplanes based at U.S. installations in the Persian Gulf. The remainder have been conducted by Navy warplanes operating from an aircraft carrier strike group in the Gulf.

The military has been conducting enhanced surveillance over Iraq since June, but officials acknowledged that they still have only a hazy idea of the Islamic State’s overall military strength and how many fighters it has in its ranks.

Hunting down the group’s leaders is expected to be an especially difficult task that would involve dedicated drone missions for weeks or months, as well as solid leads from sources on the ground.

“Doing that type of really precise targeting that you’ve seen us do in Afghanistan and Iraq previously takes a substantial amount of . . . resources,” said James O. Poss, a retired Air Force major general who oversaw drone operations and intelligence collection. “That takes time to build up that intelligence picture. It takes more than just sending an aircraft there to look around.”

The U.S. government publicly identified Baghdadi as the leader of al-Qaeda in Iraq in 2011 and offered a $10 million reward for information that would bring him “to justice.” The group has since changed its name to the Islamic State and distanced itself from al-Qaeda, although its root ideology is similar.