Strike at 'death network'

American warplanes pounded Islamic State positions in Syria for a second day yesterday as President Barack Obama called on the world to join the US-led coalition to defeat jihadists.

Obama vowed to keep up the military pressure on Islamic State militants, whose rapid rise and seizure of broad swaths of Syria and Iran stunned the Middle East and prompted five Arab states to join the US in military strikes.

Speaking at the UN General Assembly, Obama said Islamic State must be destroyed.

He also urged those who have joined the extremist group to "leave the battlefield while they can".

Before he spoke, US-led air strikes for the third time this week pounded Islamic State targets in Syria and Iraq, but the strikes did not halt the fighters' advance in a Kurdish area where fleeing refugees told of villages burnt and captives beheaded.

"The only language understood by killers like this is the language of force. So the US will work with a broad coalition to dismantle this network of death," Obama said.

Algerian militants, meanwhile, released a video that appears to show them killing Frenchman Herve Gourdel, who was kidnapped on Sunday, in what the group said was a response to France's action against IS militants in Iraq.

The US munitions used in Syria in a few days rivalled the total in the first month of attacks on the extremist group in Iraq.

Five air strikes using attack, bomber and fighter aircraft were conducted late on Tuesday and yesterday, destroying eight vehicles in Syria northwest of Al Qa'im as well as armed vehicles and a weapons cache near Baghdad and fighting positions southeast of Erbil, according to a statement from US Central Command.

The offensive two nights ago, joined by five Arab nations, used about 200 munitions, most precision-guided, as well as 47 Tomahawk cruise missiles that were launched from two warships, according to US Central Command. That rivals the 253 bombs and missiles aimed at the Sunni terrorist group's positions in Iraq from August 8 to September 10.

As US officials provided limited details on the weapons used over Syria, the F-22 Raptor, a stealth fighter made by Lockheed Martin , made its debut in warfare almost 11 years after it was declared combat-ready.

The barrage dwarfed the air strikes in Iraq so far under Obama, some of which took out targets as small as a single Humvee.

The campaign against Islamic State marks the first direct involvement of the US in Syria's conflict, which started as a peaceful protest in 2011 but degenerated into civil war.