US aircraft fighting ISIS (file)
US aircraft fighting ISIS (file)Reuters

The US-led air campaign against the Islamic State terrorist group in Iraq and Syria has killed 553 jihadis, according to the London-based Syrian Observatory for Human Rights.

According to the Observatory, 464 of that number belonged to the Islamic State - also known as ISIS or ISIL - while a further 57 were members of Al Qaeda's official branch in Syria, the Nusra Front.

32 civilians were also reportedly killed, including five women and six children. It is unclear whether the figure of 553 includes the civilians killed, or if the remainder of that number were members of other Islamist rebel groups - possibly including the Al Qaeda-sympathetic Ahrar al-Sham, which was targeted in at least one US airstrike in Syria.

On Saturday, US Central Command spokesman Colonel Patrick Ryder insisted that Washington took "reports of civilian casualties or damage to civilian facilities seriously, and we have a process to investigate each allegation."

The air campaign has had some success in rolling-back some of ISIS's dramatic gains in Iraq and Syria by working with a variety of militias and pro-government forces in Iraq. In Syria, airstrikes helped Kurdish fighters fend off an ISIS assault on the city of Kobane, along the Turkish border. Fierce fighting there is still ongoing though as Islamist forces continue to surround the embattled city.

But experts and US officials alike agree that air power alone will not be enough to defeat ISIS - which has made slight gains in western Iraq even as it has been pushed out of other places - and that a coordinated ground effort by anti-ISIS groups in both Iraq and Syria will be needed to achieve a comprehensive victory.

Western states have ruled out the possibility of sending their own ground forces to the front lines, although limited numbers of military advisers from several western countries are present in Iraq to aid Kurdish Peshmerga fighters.