An Algerian group linked to Islamic State jihadists on Monday claimed the kidnapping of a French national and threatened to kill the hostage within 24 hours unless Paris halts air strikes on the IS in Iraq.
Jund al-Khilifa (Soldiers of the Caliphate) posted a video showing the white-haired and bespectacled hostage, Herve Pierre Gourdel, squatting on the ground flanked by two hooded men clutching Kalashnikov assault rifles.
The footage was confirmed as authentic by the French government, and came after IS issued a statement urging Muslims to kill Westerners whose nations have joined a campaign to battle the jihadist group.
The United States has built a broad coalition of more than 50 nations to fight the IS organisation, after the jihadists seized large parts of Syria and Iraq and committed widespread atrocities including beheadings and crucifixions.
The jihadists are now advancing on a key border town in northern Syria, sending 130,000 terrified residents fleeing to Turkey.
- Call to kill 'disbelieving' -
In a statement posted online, IS spokesman Abu Mohamed al-Adnani said Muslims should seek out and kill Westerners whose countries have joined the coalition, in particular Americans and the French.
"If you can kill a disbelieving American or European... including the citizens of the countries that entered into a coalition against the Islamic State, then rely upon Allah, and kill him," he said.
France sought to reassure its citizens with Interior Minister Bernard Cazeneuve saying: "France is not afraid... France is prepared to respond to their threat."
Jund al-Khilifa, which has pledged allegiance to IS, raised the pressure on Paris with a threat to kill hostage Gourdel within a day.
The group said it had snatched the man in a mountainous region of eastern Algeria where Al-Qaeda is active and that it was responding to the IS call to target citizens of the coalition.
"The threats made by this group are extremely grave and demonstrate the extreme cruelty of (the IS group) and all those associated with it," French Foreign Minister Laurent Fabius said.
France is the only country so far to have joined the US air strikes against the IS in Iraq, mounting its first aerial assault against the militants on Friday.
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On Monday, Australia said it was deploying warplanes to join the aerial campaign in northern Iraq.
The announcement comes after Australian police last week foiled an alleged plot by IS jihadists to conduct "demonstration killings" in the country, including randomly beheading members of the public.
Canada, another member of the coalition, said it was looking to scale up its fight against terrorism.
- Battle to defend Kurdish town -
On the ground, Kurdish militia battling to defend Ain al-Arab, or Kobane, Syria's third-largest Kurdish town, finally appeared to be slowing the jihadists after losing ground for days.
The Syrian Observatory for Human Rights said Kurdish forces, backed by Syrian Arab rebels, had intensified their attacks against IS fighters, killing 21 jihadists overnight.
IS aims to seize Ain al-Arab to secure its grip over a long stretch of Syria's northern border with Turkey.
It has battled Kurdish forces in northern and western Syria, viewing the minority as apostates, even though they are also Sunni Muslims, because of their secular outlook.
The Observatory said Monday the jihadists had seized at least 64 villages around Ain al-Arab and executed at least 16 Kurds.
The PKK Kurdish rebel group in Turkey has called on Kurds to cross into Syria to help in the battle, but Turkish officials have tightly controlled the border.
After an initial flood at the weekend when guards cut barbed wire on the border, Ankara has limited entries to only three crossings and prevented some from going into Syria.
For a second day, Kurdish protesters angry over the Turkish move were seen clashing near the border with security forces who again fired tear gas and used water cannon to disperse them.
Syrian opposition officials and Kurdish activists have called for international intervention by the US-led coalition assembled to fight IS.
Washington has said it would consider strikes against IS in Syria, even without permission from Damascus, but its UN envoy said Sunday "no decisions" had been taken.