US President Barack Obama met the head of Iraq's autonomous Kurdish region at the White House on Tuesday, courting a vital ally on the frontline of the fight against Islamic militants.

Obama and Vice President Joe Biden met Massud Barzani to discuss the campaign to regain Iraqi territory lost to the Islamic State group.

A US-led coalition has carried out more than 3,000 air strikes over Iraq since September in a bid to dislodge the jihadists.

On the ground, battle lines have been drawn in Anbar province and the northern city of Mosul, where Kurdish fighters are likely to play a key role in a looming offensive.

The city, a short distance from the Kurdish capital Arbil, holds special significance for the Islamic State militants.

It was there that IS leader Abu Bakr al-Baghdadi proclaimed his "caliphate" straddling Iraq and Syria.

Some 4,000-6,000 Iraqis -- many of whom fled the IS capture of Mosul -- are now being trained in Iraqi Kurdistan for the upcoming battle to retake the city.

In a statement, the White House said Obama "commended the bravery of the Kurdish peshmerga (forces)."

But amid sensitivities over Kurdish self-rule, the White House did not allow the media to witness the meeting and said Obama "dropped by."

Barzani's last visit to Washington dates back to April 2012.

The meeting comes only weeks after a landmark visit by Iraqi Prime Minister Haider al-Abadi.

The Kurdish leader is on a week-long visit which will also include talks on Wednesday with state department officials.