UK raises terror threat level

British Prime Minister David Cameron told reporters there was "no doubt in my mind" that jihadists from the Islamic State (IS) group in Iraq and Syria had their sights set on targets in Europe.

Britain raised its terror threat alert level to "severe", meaning an attack is "highly likely".

Despite the move, White House spokesman Josh Earnest said Washington had no plans to follow suit, but US national security officials had been in close contact with London on the issue.

US President Barack Obama has admitted that he has no immediate strategy to tackle advancing IS jihadists.

In Geneva, UN refugee agency chief Antonio Guterres said Syria had become the "biggest humanitarian emergency of our era" after a million people joined the exodus in the past year alone.

They have fled the war-wracked country where jihadists have sown panic with atrocities and executions, including this month of scores of Syrian soldiers and a US journalist.

The scale of the crisis facing the international community deepened after rival Islamists led by Al-Qaeda's Syria affiliate, Al-Nusra Front, seized 44 Fijian UN peacekeepers on the Golan Heights.

"The latest information we have is that they are safe and I can say now that the negotiations for their release have already begun," Fiji's Prime Minister Voreqe Bainimarama said.

The militants also surrounded 72 Filipino peacekeepers, sparking a tense standoff for the UN mission that has monitored a Syrian-Israeli armistice for decades.

Manila said its troops besieged by rebels were ready to use "deadly force" to defend themselves.

A United Nations spokesman said that assurances had been received that all were safe and in good health amid efforts to secure their release.

The UN Security Council demanded the "unconditional and immediate release" of the peacekeepers.

Twice last year peacekeepers were detained before being freed.

Dampening prospects of imminent air strikes in Syria, Obama said he was still developing a comprehensive plan to defeat IS, which has overrun large swathes of Iraq and neighbouring Syria.

"We don't have a strategy yet," Obama said, adding that he was sending Secretary of State John Kerry to the Middle East to build regional support against IS.

The Syria war has killed some 191,000 people since March 2011 but has taken on a new dimension as IS unleashed a shocking brutality.

Washington has launched air strikes in Iraq that have helped Kurdish forces claw back some territory lost to the jihadists earlier this month.

The Pentagon said the US military's operations in Iraq cost an average of $7.5 million a day.

The American campaign has infuriated the jihadists who posted grisly video footage Thursday of their execution of a Kurdish fighter.

The video also shows other captive Kurds warning that they risk the same fate.

It follows another jihadist video showing scores of bodies in the desert that IS boasted were Syrian soldiers it captured and killed.

The jihadists have also carried out a spate of executions of civilians from religious minorities in northern Iraq.

On Friday, Iraqi aircraft struck jihadists besieging the Shiite Turkmen town of Amerli for more than two months, as government forces readied an offensive, officers said.

Amerli residents are in grave danger both because of their Shiite faith, which jihadists consider heresy, and their resistance to the militants, which has drawn harsh retribution elsewhere.

"Whole communities that had lived for generations in northern Iraq are being forced to flee or face death just for their religious beliefs," UN chief Ban Ki-moon said Friday.

His comment came as the International Organization for Migration said that more than 1.6 million Iraqis have been displaced this year, more than 850,000 this month alone.

"Many of their loved ones were killed or abducted by IS forces. Groups of people were reportedly forced by IS to jump off mountain cliffs, while others were taken away to an uncertain fate," said IOM emergency coordinator for Iraq Brian Kelly.

A UN-mandated probe has charged that public executions, amputations, lashings and mock crucifixions have become commonplace in jihadist-controlled areas of Syria.

Meanwhile, Hollywood star and UN refugee agency goodwill ambassador Angelina Jolie made a plea for the end of Syria's three-and-a-half year war.

"Three million refugees is not just another statistic. It is a searing indictment of our collective failure to end the war in Syria," she said.