Several hundred Yazidi captives have been killed in Iraq by Islamic State (IS) militants west of Mosul, Yazidi and Iraqi officials say.

A statement from the Yazidi Progress Party said 300 captives were killed on Friday in the Tal Afar district near the city.

Iraqi Vice-President Osama al-Nujaifi described the reported deaths as "horrific and barbaric".

Thousands of members of the religious minority group were captured last year.

It is not clear how they were killed, or why this has happened now, says the BBC's Middle East editor Alan Johnston.

Many are reported to have been held in Mosul, the main stronghold of IS after the militants swept through large areas of northern and western Iraq, and eastern Syria in 2014.

Yazidis, whose religion includes elements of several faiths, are considered infidels by IS.

Thousands fled to the Kurdish-controlled region of northern Iraq after IS captured the Yazidi-populated Sinjar district in Nineveh province.

Hundreds of men were killed, while some Yazidi women were held and used as sex slaves.

IS PUSHED BACK

The Yazidi Progress Party's statement, quoted by the Kurdish Shafaq News website, condemned the latest incident as a "heinous crime" and called on Iraqi forces to free those still held by IS.

In January, IS released some 200 mainly elderly Yazidis into the hands of Kurdish officials near the city of Kirkuk.

Many of them, held in Mosul, had disabilities or were wounded, though no reason was given by IS for their release.

In recent months, IS has been pushed back from some of the areas it captured, though many Yazidi villages are thought to remain under the militants' control.

In December, Kurdish Peshmerga forces drove back IS militants in north-western Iraq, relieving a long siege of Sinjar mountain where thousands of Yazidis had sought refuge.

The Iraqi government, with forces backed by Iran, also declared it had taken back control of the city of Tikrit in April.