WASHINGTON - American special operations forces killed a senior Islamic State leader in a raid in Syria, US officials said on Saturday, an operation that marked a departure from Washington's strategy of relying primarily on air strikes to target militants there.

Delta Force commandos used UH-60 Black Hawk helicopters and V-22 Osprey tiltrotor aircraft to punch deep into eastern Syria from Iraq. They engaged in a firefight and hand-to-hand combat with Islamic State fighters, killed a key figure in the group named as Abu Sayyaf and captured his wife, US officials said.

The officials described Sayyaf, a Tunisian, as an Islamic State commander who helped manage the group's black-market sales of oil and gas to raise funds. The officials said President Barack Obama ordered the overnight operation, which killed about a dozen Islamic State fighters and had been planned for several weeks.

It marked the first known US special forces operation inside Syria apart from a failed mission last year to rescue US and other foreign hostages held by Islamic State in northeastern Syria.

Wary of the United States getting pulled deeper into Middle East conflicts, Obama has promised not to commit major ground forces in the fight against Islamic State, which has seized swathes of Syria and Iraq. But he has left open the prospect of special forces raids.

It was not immediately clear if this one marked the start of a new chapter in Syria.

US and Arab forces have carried out almost daily air raids against hardline Islamist militant groups in Syria including Islamic State since last September, and US-led forces are also targeting the group in Iraq.

Defense Secretary Ash Carter said the operation was intended to capture Abu Sayyaf but he was killed "when he engaged US forces." His wife, Umm Sayyaf, was captured, then placed in US military detention in Iraq and was being questioned about Islamic State operations and hostages held by the group.