Iraqi Kurdish leader Massud Barzani hailed victories over the Islamic State jihadist group during a visit on Sunday to Mount Sinjar, which had been besieged by the militants for months.

Thousands of the autonomous Kurdish region's peshmerga fighters launched a major operation backed by U.S.-led air strikes on Wednesday which broke the second IS siege of Mount Sinjar this year.

The Yazidis are a small, misunderstood and long-persecuted religious sect rooted in the town of Sinjar, in northern Iraq, and in parts of Syria and Turkey.

No one knows the exact size of the Yazidi population. Estimates range from tens of thousands to 500,000 or more. Over centuries, they have been the target of violence and purges, including during the Ottoman empire, and have survived as a close-knit community that does not proselytize.

The outlawed Kurdistan Workers' Party (PKK), which for years waged a deadly insurgency against Turkish authorities, called on all Kurdish armed groups Tuesday to unite against radical Islamist militants who have seized swathes of northern Iraq.

"Our efforts alone are not enough. There must be a joint (effort)" against the Islamic State (IS), the PKK's military leader Murat Karayilan said in remarks carried by the Radikal online newspaper.

The capture of the Iraqi town of Sinjar by jihadist fighters has sent up to 200,000 people into flight and sparked a "humanitarian tragedy" amid fears for their lives, the United Nations said Sunday.

"A humanitarian tragedy is unfolding in Sinjar," the top UN envoy in Iraq, Nickolay Mladenov, said in a statement after the Islamic State (IS) group captured the northern town, which lies near the Syrian border and was already home to thousands of previously displaced families.