French President Francois Hollande. (Getty)  Paris will not make any concessions to jihadists who have threatened to kill a French hostage in Algeria, President Francois Hollande says.  "As grave as this situation is, we will not give into any blackmail, any pressure, any ultimatum no matter how odious, how despicable," he said, vowing continued support for Iraqi authorities battling jihadists.  Jund al-Khilifa or "Soldiers of the Caliphate", a group linked to Islamic State jihadists, kidnapped 55-year-old hiker Herve Gourdel on Sunday and vowed to kill him on Tuesday unless Paris halts air strikes in Iraq.  Speaking to French reporters on the sidelines of the UN climate summit in New York, Mr Hollande said he had spoken to the Algerian prime minister on Monday night in order to cooperate and share all useful information.  Algerian military planes have been combing the mountainous eastern Tizi Ouzou region backed by elite anti-terrorist troops in a desperate bid to find Mr Gourdel, a security source said.  As the deadline loomed, some 20 truckloads of paratroopers also joined the search, a witness said, and police set up roadblocks along the highway that works its way through the mountains.  "I have full confidence that the Algerian security forces are doing everything possible so that we can find our compatriot," Mr Hollande said.  He also praised the "dignity and courage" of Mr Gourdel's family and said he had spoken on Tuesday morning to his parents.  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.  While the United States launched strikes against the Islamic State jihadists in Syria, France has said it will limit its strikes to Iraq.  Do you have any news photos or videos?
The search is continuing in Algeria for a Frenchman being held hostage by an IS-linked group that has threatened to execute him.