Fighters from the Islamic State of Iraq and the Levant (ISIL) have continued to advance into the Kurdish-dominated town of Ain al-Arab in Syria, despite the U.S.-led air campaign against the Al-Qaeda-linked group.

The U.S. Central Command said the airstrikes destroyed an ISIL building and two armed vehicles near the border town of Kobane, which the insurgents have been besieging for the past 10 days.

It said an airfield, garrison and training camp near the ISIL stronghold of Raqqa were also among the targets damaged in seven airstrikes conducted by the United States, Saudi Arabia, Jordan and the United Arab Emirates, using fighter planes and remotely piloted aircraft.

The U.S. has been carrying out strikes in Iraq since Aug. 8 and in Syria, with the help of Arab allies, since Tuesday, in a campaign it says is aimed at "degrading and destroying" the militants who have captured swathes of both countries.

A day after the UK parliament voted to allow British warplanes to attack ISIL in Iraq, two British fighter jets flew a mission over the country, the Ministry of Defense said, adding they had gathered intelligence but did not carry out air strikes.

ISIL, which swept across northern Iraq in June, has proclaimed an Islamic "caliphate," beheaded Western hostages and ordered Shia Muslims and non-Muslims to convert or die. Its rise has prompted President Barack Obama to order U.S. forces back into Iraq, which they left in 2011, and to go into action over Syria for the first time.

The Syrian Observatory for Human Rights, a monitoring group that supports opposition forces fighting Syrian President Bashar al-Assad, said Saturday's air strikes set off more than 30 explosions in Raqqa.

Rami Abdulrahman, who runs the British-based Observatory, said 23 Islamic State fighters were killed. He said the heaviest casualties were inflicted in attacks on an airport.

But the monitoring group said ISIL was still able to shell eastern parts of Kobane, wounding several people, in a sign that its fighters were drawing closer. The insurgents' weeklong offensive against the Kurdish town has prompted about 150,000 people to pour across the border into Turkey.