Turkey on Tuesday indicated that dozens of Turkish hostages abducted by Islamic State (IS) insurgents in Iraq may have been freed in exchange for the release of IS militants held by Syrian rebels.

Citing security sources, the Hurriyet daily said that Syrian rebels released 50 members of IS, including the family of a key radical leader, in exchange for the release of Turkish hostages.

Paris will not make any concessions to jihadists who have threatened to kill a French hostage in Algeria, President Francois Hollande said Tuesday.

"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 to continued support for Iraqi authorities battling jihadists.

Israel downed a Syrian warplane over the Golan Heights on Tuesday in the first such incident in three decades and warned it would respond "forcefully" if its security is threatened.

It was the first time Israel had shot down a piloted Syrian plane since 1985 and drew a sharp response from Damascus.

Syria's opposition National Coalition on Tuesday welcomed U.S.-led air strikes against the Islamic State group, but urged sustained pressure on President Bashar Assad's government.

"Tonight, the international community has joined our fight against ISIS in Syria," Coalition president Hadi al-Bahra said, using an alternative acronym for the jihadist group.

Foreign Minister Julie Bishop on Tuesday said Canberra was treating as genuine a call by the Islamic State group for Muslims to indiscriminately kill Australians, issued after anti-terrorism raids foiled an alleged abduction plot.

The militants on Monday released a statement urging the deaths of citizens of all countries taking part in the U.S.-led coalition against the jihadists. Australia was mentioned, along with the United States, Canada and France. 

The United States and its Arab allies unleashed deadly bomb and missile strikes on jihadists in Syria on Tuesday, opening a new front in the battle against the Islamic State group.

Dozens of IS and Al-Qaida militants were reported to have been killed in the raids, which Washington said had partly targeted extremists plotting an "imminent attack" against the West.

Syria's opposition on Monday called for air strikes to be immediately launched against Islamist fighters who have captured villages in the north -- or risk "catastrophe."

"We must begin air strikes immediately in Syria," Syrian National Coalition president Hadi al-Bahra told a news conference at U.N. headquarters in New York.

France's foreign minister hit out Monday at Tony Blair's statement that sending ground troops to fight the Islamic State group should not be ruled out, saying he was not "best placed" to comment.

The former British prime minister, who sent troops to invade Iraq in 2003, wrote in an essay on the website of the Tony Blair Faith Foundation that Western powers should not rule out ground engagement "in the future if it is absolutely necessary".

Osmane Sero has been at it since dawn, pacing back and forth in front of a line of Turkish police by the border with Syria.

Clutched in his wrinkled hand is his Syrian passport and a photograph of a smiling five-year-old girl.

Islam has been tarnished by "forces of darkness" and Saudi Arabia should do more to protect its youth from violent extremism, the kingdom's second crown prince said on Monday.

The comments by Crown Prince Moqren bin Abdul Aziz, in a speech for Saudi Arabia's 84th national day Tuesday, come after the kingdom this month agreed with other Arab states to back Washington against Islamic State group jihadists.