The US-led air campaign against terrorists in Syria amounts to a war against Islam, Al-Qaeda-linked Nusra Front group has claimed, promising retaliation against those states involved in the bombing of the ‘caliphate’ instead of targeting Assad forces.

“We are in a long war. This war will not end in months nor years,” group spokesman Abu Firas al-Suri said as cited by Reuters. “It's not a war against Nusra Front, it's a war against Islam.”

Dozens of Al-Nusra Front fighters were reportedly killed after the anti-ISIS coalition launched the first round of its airstrikes on Tuesday, and the audio message released on Saturday is the group’s first reaction to attacks.

“These countries have done a despicable act that will put them on the list of those targeted by jihadist forces all over the world,” the spokesman added.

The United States and its five Arab allies – Saudi Arabia, Qatar, Jordan, Bahrain and the United Arab Emirates – all participated in the campaign in Syria while over 50 states expressed their general support for the coalition's fight against the Islamic State threat. So far European allies have been more cautious than the US, with the UK and France only bombing targets in Iraq, which actually requested international intervention, unlike Syria which has only been “informed” about the forthcoming operation on its soil.

Besides the Islamic State jihadist fighters, the US airstrikes have also separately targeted an Al-Qaeda-affiliated terror group that US officials fear is plotting attacks on the West. While regularly reporting its progress at “degrading and destroying” the militants, the US military officials deny that any civilian casualties took place so far, despite numerous reports from activists on the ground.

People in the rebel-held northern provinces in the meantime have been protesting massively against the US-strikes they claim are killing not only the terrorists but civilians too, while completely ignoring the targets associated with the Syrian government.

Numerous videos of such demonstrations held after Friday prayers appeared on YouTube, with some people questioning the US airstrike strategy which so far failed to cripple Assad's military power, while others were expressing support for the creation of the Islamic caliphate.

“Down with America!” shouted hundreds of men supporting the Al-Qaeda linked group in the city of Maaret al-Numan, according to the Wall Street Journal. “With our soul and blood we defend you, Nusra!”

But besides the groups classified as terrorist organizations by the US, the West-backed Harakat Hazm rebel group also criticized the strikes earlier this week.

“The sole beneficiary of this foreign interference in Syria is the [President Bashar] Assad regime, especially in the absence of any real strategy to topple him,” said the group of an estimated 7,000 fighters, describing the strikes as “an attack on national sovereignty that undermines the Syrian revolution.”

Meanwhile US military officials announced that air attacks on IS strongholds in Syria was not enough and a ground campaign was needed to crush the terrorists. And such force would be the so-called "moderate opposition" trained and equipped by the US.

READ MORE:Pentagon ready to train up to 15,000 Syrian rebels

“Yes, there has to be a ground component to the campaign against ISIL in Syria,” Joint Chiefs of Staff Chairman Gen. Martin Dempsey said, adding that earlier figures pertaining to a group of 5,000 prospective US-trained forces may be but a fraction of what is truly required to degrade and destroy the Islamic State.