US Vice-President Joe Biden delivers an address on US policy in Iraq in advance of Iraqi Prime Minister Haider al-Abadi's visit, at the National Defense University, Washington DC, April 9, 2015. [Photo/Xinhua]

WASHINGTON - US Vice-President Joseph Biden said on Thursday that US-led airstrikes have helped Iraqi forces halt the offensive by the extremist Islamic State (IS) group in the Arab country, with its "aura of invincibility" pierced.

"The jury's still out," Biden said at the National Defense University in Washington DC. "It's not over yet, but the momentum is in the right direction."

Washington began airstrikes on IS targets inside Iraq on Aug 8 last year and has sent back some 3,000 troops in its efforts to stem the lightening advances by the militants there.

"Eight months ago, ISIL was on the offensive everywhere in Iraq," Biden said, using IS' another name. "But today in Iraq, ISIL has lost large areas that it used to dominate. ISIL's momentum in Iraq has been halted and in many places ... has been flat-out reversed. "

"I don't want to paint an overly rosy picture, but ISIL's aura of invincibility has been pierced," he added.

Washington and Baghdad were reportedly divided over where to go after the Iraqi forces retook the city of Tikrit last week under the cover of US-led air raids.

Iraqi security forces started an offensive in the western province of Anbar on Wednesday instead of preying on Mosul, Iraq's second largest city now under IS' control, as suggested by US officials.

Iraqi Prime Minister Haider al-Abadi is scheduled to make his first trip to the United States next week and meet with US President Barack Obama.