The number of refugees from the conflict in Syria now tops three million, the United Nations said Friday, as US President Barack Obama admitted he still has no strategy to tackle advancing jihadists.
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, as Islamic State (IS) fighters seized swathes of the northeast.
The jihadists have sown panic with a spate of atrocities, executing more than 160 captured Syrian soldiers and an Iraqi Kurdish fighter over the past week, following its brutal beheading of US journalist James Foley earlier this month.
The scale of the crisis facing the international community was further highlighted by the seizure by rival Islamists led by Al-Qaeda of 43 UN peacekeepers on the Golan Heights.
The militants also surrounded another 75 peacekeepers from the Philippines, triggering a tense standoff for the UN mission that has monitored an armistice between Syrian and Israeli troops on the strategic plateau for decades.
Dampening hopes of imminent air strikes in Syria, Obama said he was still developing a comprehensive plan to defeat IS, which has also overrun large swathes of neighbouring Iraq.
The civil war in Syria has killed some 191,000 people since it erupted in March 2011 with President Bashar al-Assad's bloody effort to put down an uprising.
But it has taken on another dimension as IS jihadists exploited the power vacuum to move in, unleashing a series of atrocities that have shocked the world.
"We don't have a strategy yet," Obama said ahead of a meeting with security chiefs.
But he said he was dispatching Secretary of State John Kerry to the Middle East to build support in the region against IS.
Washington has carried out air strikes in neighboring Iraq that have helped Kurdish forces to claw back some of the territory they lost to a renewed offensive by the jihadists earlier this month.
The Iraqi Kurdish leadership's military cooperation with the United States has infuriated the jihadists who posted grisly video footage on Thursday of their execution of a Kurdish fighter outside a mosque.
The video, titled "A message in blood to the leaders of the American-Kurdish alliance," also shows other captive Kurdish fighters warning that they risk the same fate if the cooperation continues, the SITE Intelligence Group monitoring service said.
The prisoners were paraded in orange jumpsuits of the sort used at the US detention centre in Guantanamo Bay, Cuba where hundreds of jihadists were interned during Washington's "war on terror".
The video comes hot on the heels of footage of scores of bodies heaped in the desert that IS boasted were those of Syrian soldiers it captured and killed following its seizure of a key air base last weekend.
The jihadists have also carried out a spate of executions of civilians from religious minority groups in northern Iraq since they went back on the offensive.
UN chief Ban Ki-moon added his voice Friday to a chorus of international condemnation.
"Whole communities that had lived for generations in northern Iraq are being forced to flee or face death just for their religious beliefs," he said.
The International Organization for Migration said Friday that over 1.6 million Iraqis have been displaced this year, more than 850,000 of them this month alone.
"Most of the internally displaced had to walk for several days to reach safety," said the group's emergency coordinator for Iraq, Brian Kelly.
"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."
A UN-mandated probe has charged that public executions, amputations, lashings and mock crucifixions have also become a regular fixture in jihadist-controlled areas of Syria.
Washington has so far baulked at cooperating with Assad's regime against IS.
Obama reiterated that position on Thursday, saying: "I don't think there's a situation where we have to choose between Assad or the kinds of people who carry on the incredible violence that we've been seeing there."
Al-Nusra Front, backed by other rebels, detained 43 UN peacekeepers on the Golan on Thursday, a day after their capture of the sole crossing over the UN-patrolled armistice line to the Israeli-occupied sector of the plateau.
The peacekeepers from Fiji were forced to surrender their weapons and taken hostage, but 75 Filipino blue helmets "held their ground" and refused to disarm, the Philippine defense department said.
The commander of the Philippines' peacekeeping operations division, Colonel Roberto Ancan, said no shots had been fired but the troops were authorized to use deadly force in defense of their bases.
The UN Security Council condemned the action and demanded the "unconditional and immediate release" of the peacekeepers.
Peacekeepers were detained twice last year before being released safely.
The Philippines said before the latest incident that it will repatriate its 331-strong contingent for security reasons, mirroring previous moves by Australia, Croatia and Japan.