The United States is poised to send spy planes into Syria to track Islamic State jihadists, whose advances have sparked international concern and US airstrikes in neighboring Iraq.

A US official confirmed the plans after Syria said on Monday it was willing to work with the international community, including Washington, to tackle extremist fighters.

But US officials said they did not plan to ask Damascus for permission despite Syrian insistence that any military action on its soil must be coordinated in advance.

International concern about the Islamic State has been rising after a lightning offensive by the group through parts of Iraq and a string of brutal abuses, including the murder of US journalist James Foley.

The United Nations has accused the Islamic State and affiliated groups in Iraq of carrying out "ethnic and religious cleansing" that could amount to crimes against humanity.

On Monday, Damascus said for the first time that it was willing to work with the international community, including the US and Britain, to tackle "terrorists", including the Islamic State and al-Qaida's Syrian affiliate, al-Nusra Front.

Syria seeks cooperation

But Syrian Foreign Minister Walid Muallem also made it clear that Syria will not accept unilateral military strikes by the US or any other country.

"Any violation of Syria's sovereignty would be an act of aggression," he said.

There would be "no justification" for strikes on Syrian territory "except in coordination with us to fight terrorism".

Muallem said Syria was seeking cooperation within an international or regional coalition, or at the bilateral level within the framework of a recent UN Security Council resolution targeting the Islamic State and al-Nusra.

But it remains unclear whether the international community will be willing to cooperate publicly with President Bashar al-Assad's government, which has been engaged in an effort to put down a civil war that began in March 2011.

Washington has accused Assad's government of using chemical weapons and carrying out other widespread abuses.

International concern about the Islamic State has also grown, with Washington beginning airstrikes against the group in Iraq on Aug 8 in a bid to roll back its advances.

US Chairman of the Joint Chiefs of Staff General Martin Dempsey acknowledged after the strikes began that the Islamic State cannot be defeated in Iraq alone.

Fears heightened

"Can they be defeated without addressing that part of the organization that resides in Syria? The answer is no," he said.

The White House says that no decision has been taken on whether to carry out airstrikes in Syria.

But US aircraft have already entered Syrian airspace covertly at least once, during a failed bid to rescue hostages including Foley who was later beheaded by Islamic State militants.

Foley's murder and advances by the Islamic State in both Syria and Iraq have heightened fears about the group, which emerged from al-Qaida's one-time Iraqi affiliate but has since parted ways.

UN human rights chief Navi Pillay said Monday that the Islamic State and affiliated groups in Iraq were "systematically targeting men, women and children based on their ethnic, religious or sectarian affiliation and are ruthlessly carrying out widespread ethnic and religious cleansing.

"Such persecution would amount to crimes against humanity," she said.

On Sunday, the Islamic State cemented its control over an entire province in Syria for the first time, seizing the Tabqa military airport in a bloody battle that killed hundreds of people.

The air base was the last outpost controlled by the Syrian military in Raqa province, which has now become an Islamic State stronghold.