The UN Monday accused jihadists in Iraq of waging a campaign of "ethnic and religious cleansing", as Syria said it was ready to work with the global community against "terrorism".

The accusation by UN human rights chief Navi Pillay came as Kurdish peshmerga forces pushed back Islamic State (IS) jihadists northeast of Baghdad a day after the militants overran a key military airport in Syria.

Pillay said in a statement the IS reign of terror in Iraq against non-Arab ethnic groups and non-Sunni Muslims alike involved targeted killings, forced conversions, abductions, trafficking, and destruction of holy and cultural sites.

"They are systematically targeting men, women and children based on their ethnic, religious or sectarian affiliation and are ruthlessly carrying out widespread ethnic and religious cleansing in the areas under their control," Pillay said.

"Such persecution would amount to crimes against humanity," she added, as the UN Committee for the Elimination of Racial Discrimination urged the 47 nations that make up the UN Human Rights Council to hold an emergency session on the crisis.

The watchdog also said it was time for the UN Security Council to deploy a "peace force" to create a "safe zone" around Nineveh.

Iraq is struggling to regain significant parts of the country after the jihadists led a lightning militant offensive, seizing second city Mosul in June and sweeping through the country's Sunni heartland, as security forces fled.

The IS militants have also taken control of swathes of neighbouring Syria contiguous to the land seized in Iraq, declaring an Islamic "caliphate" straddling both countries.

- 'Syria ready for cooperation' -

Syria, locked in a civil war with various rebel groups including IS since March 2011, said Monday for the first time it will work with the international community, including the United States, to tackle the problem.

Foreign Minister Walid Muallem insisted at a news conference in Syria's capital, however, that any strikes on its territory must be coordinated with Damascus.

"Syria is ready for cooperation and coordination at the regional and international level to fight terrorism and implement UN Security Council resolution 2170," Muallem said.

The resolution, passed earlier this month, seeks to cut funds and the flow of foreign fighters both to the Islamic State and to Al-Qaeda's Syrian affiliate, Al-Nusra Front.

Western powers fear the IS "caliphate" -- a successor state to historic Muslim empires -- could become a launchpad for a new round of global terror attacks.

Those fears were exacerbated by the grisly IS beheading of American journalist James Foley who was abducted in Syria.

Washington has ramped up its rhetoric following the beheading, calling it "a terrorist attack against our country" and said operations against the group in Syria may also be necessary.

US air strikes have allowed the peshmerga to claw back some lost territory, but the campaign has so far been limited to northern Iraq.

Citizens from various western countries are fighting with IS, further raising fears that they could carry out attacks at home.

In a statement Sunday claiming a string of attacks in the northern Iraqi city of Kirkuk that killed 24 people the previous day, IS identified two of the three suicide bombers as German.

- Peshmerga retake villages -

On Monday, the peshmerga retook three villages in the Jalawla area northeast of Baghdad from jihadist militants and also held off two assaults elsewhere, officials said.

The Kurdish fighters also took control of a main road used by jihadists to transport fighters and supplies, peshmerga members said.

In Syria, the jihadists on Sunday won a bloody battle for the Tabqa military airport, the last stronghold of the Damascus regime in the northern province of Raqa, a monitoring group and state media said.

The Syrian Observatory for Human Rights said 346 jihadists and almost 200 Syrian troops were killed in the six-day battle for the airport.

The victory gives the IS jihadists full control of Raqa, the heartland of their "caliphate".

On Monday, a suicide bomber attacked Shiite worshippers during prayers in eastern Baghdad, killing 11 people, security and medical officials said.

The attack, which targeted a Shiite place of worship, or husseiniyah, also wounded 32 people, the officials said.

It comes three days after suspected Shiite militiamen gunned down 70 Sunni worshippers at a mosque northeast of the capital.

Premier-designate Haidar al-Abadi said there is no place for weapons or armed groups outside Iraqi state control, in the wake of the Sunni mosque attack.

"I confirm that weapons must remain in the hand of the state -- there is no place for any armed group," he told a news conference on Monday.

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