BAGHDAD (AFP) - Syria said it was ready to work with the United States to fight "terrorism" as the UN accused jihadists in Iraq of "ethnic and religious cleansing".

The United States is poised to send spy planes into Syria to track militants, preparing the way for possible air strikes against jihadists there, a senior US official said, as the most senior US military officer warned they will soon threaten America and Europe.

The White House, however, said President Barack Obama had so far made no decision on whether to launch air strikes on Islamic State (IS) militants in Syria.

Syria, locked in a civil war with various rebel groups including IS since March 2011, said for the first time that it would work with the international community, including the United States, to tackle the Islamist problem. But Foreign Minister Walid Muallem insisted at a news conference that any strikes on Syrian territory must be coordinated with the government of President Bashar al-Assad.

"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 on Monday in the Syrian capital.

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 beheading of American journalist James Foley, who was abducted in Syria.

UN human rights chief Navi Pillay said abuses by IS and affiliated groups in Iraq against non-Arab ethnic groups and non-Sunni Muslims 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 said in a statement.

IS threat to US, Europe

Iraq is struggling to regain huge tracts of the country after the jihadists fought a lightning offensive, seizing the second city Mosul in June and sweeping through the country's Sunni heartland. The IS militants have also taken control of parts of Syria contiguous to the land seized in Iraq, declaring an Islamic "caliphate" straddling both countries.

General Martin Dempsey, chairman of the US Joint Chiefs of Staff, believes that the threat posed by the group will "soon" expand to both the United States and Europe, his spokesman said on Monday.

"He (Dempsey) believes that (IS) must be pressured both in Iraq and in Syria," Colonel Ed Thomas added.

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

US warplanes for more than two weeks have carried out a limited air campaign against the IS in Iraq, with most of the bombing raids conducted near Mosul dam in the north.

Citizens from various Western countries are fighting for 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.

Kurds retake villages

Kurdish peshmerga forces on Monday retook three villages in the Jalawla area northeast of Baghdad from militants, and also held off assaults elsewhere, officials said. In Syria, the jihadists on Sunday won a bloody battle for the Tabqa military airport, the last stronghold of the Assad regime in the northern province of Raqa, a monitoring group and state media said.

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, while at least eight died in two car bombs in the capital's north, security and medical officials said. The violence comes three days after suspected Shiite militiamen gunned down 70 Sunni worshippers at a mosque northeast of Baghdad.

After the mosque attack, premier-designate Haidar al-Abadi said there was no place for weapons or armed groups outside Iraqi state control. Abadi said he welcomes irregular forces fighting against militants, but they "must all be inside the framework of the state, and under the direction of the state, under control of the military and security forces".