WASHINGTON - US defense chief Ash Carter said on Tuesday the Pentagon was deploying a specialized operations force which would "over time" conduct unilateral operations in Iraq and Syria as part of US military campaign against the Islamic State (IS), also known as ISIL.

"These special operators will over time be able to conduct raids, free hostages, gather intelligence, and capture ISIL leaders," said Carter here in a congressional hearing, adding that the creation of the specialized operations force was a result of "full coordination" with the Iraqi government.

"The raids in Iraq will be done at the invitation of the Iraqi government and focused on defending its borders and building the ISF's (Iraqi security forces) own capability," Carter said.

Meanwhile, Carter said, the force would also be in a position to conduct unilateral operations in Syria.

"That creates a virtuous cycle of better intelligence, which generates more targets, more raids, and more momentum," he said.

Facing mounting criticism for its Syrian policy, the Obama administration had already announced its plan to send fewer than 50 US special operations troops to assist rebels in Syria.

Carter's announcement came amid the White House's repeated objection to sending ground troops to Syria and Iraq.

Despite its dismissal of having "boots on the ground" fighting the IS, the White House had argued that sending special operations forces was different from large-scale, ground combat operations.