An Australian who travelled to Syria to join Kurds battling jihadists has been killed, a monitor said Wednesday, adding he was the first Westerner to die fighting alongside the Kurds.

"An Australian man was killed in an assault on Tuesday by the Islamic State against a position of the Kurdish People's Protection Units (YPG) near Tal Hamis in Hasakeh province," said Syrian Observatory for Human Rights director Rami Abdel Rahman.

A former jihadist who became an al-Qaida double agent says Muslims must do more to tackle extremism in their midst and that stopping lone wolf attacks is near-impossible.

Morten Storm has seen deep inside the conflict between jihadists and Western intelligence services, having served both.

A leading Syrian opposition figure, Louay Hussein, said he was freed on bail on Wednesday, more than three months after he was detained.

"I just left prison, I am on my way home," Hussein told AFP in Beirut on the phone from Syria, adding that he was in good spirits.

The United States has condemned the abduction by the Islamic State group of dozens of Assyrian Christians in Syria and demanded their immediate release.

It was the first mass kidnapping of Christians in the war-torn country.

The kidnapping of dozens of Assyrian Christians by the Islamic State jihadist group in Syria has prompted an exodus of terrified families fleeing their homes, activists said Wednesday.

The United States condemned the mass abduction of Christians -- the first of its kind in the war-torn country -- and demanded the release of the 90 hostages.

Four French lawmakers met with Syrian President Bashar Assad Wednesday during a private trip to the war-torn country, despite a breakdown in diplomatic ties between Paris and Damascus.

The French government, which supports the moderate Syrian opposition and wants Assad to leave power, was quick to clarify that the lawmakers were there in no official capacity.

France said on Wednesday that it will begin shipping $3 billion worth of weapons paid for by Saudi Arabia to the Lebanese army in April.

The Defense Ministry said in a statement that the deal, first announced in 2013, will supply French armored vehicles, warships, attack helicopters, munitions and communications gear.

At a shelter in Damascus, the strain of life under a crippling siege not far from the Syrian capital is etched on the gaunt faces of those who have escaped.

Hundreds of families have fled the district of Eastern Ghouta in the past few months, after more than one-and-a-half years of hunger and deprivation.

The chain-link fences, topped with coils of barbed wire, rise and fall like a serpent's back across the desert scrubland between Saudi Arabia and the jihadist threat across the Iraqi border.

A double-fence system and complementary hi-tech surveillance tools, officially opened in September, have become the front line of efforts to protect the kingdom from Islamic State (IS) group extremists who have seized vast areas of Iraq as well as Syria.

The American public has grown more supportive of the U.S. fight against the Islamic State group, with nearly two-thirds now backing the air campaign against the jihadists, according to a survey released Tuesday.

About twice as many approve (63 percent) as disapprove (30 percent) of the military campaign against the IS group in Iraq and Syria, a national survey carried out by the Pew Research Center found.