Nusra Front fighters in Syria
Nusra Front fighters in SyriaReuters

The Al-Qaeda-linked Syrian rebel group Al-Nusra Front on Saturday denounced U.S.-led airstrikes on Syria and threatened to retaliate against Western and Arab countries that took part, Reuters reported.

"We are in a long war. This war will not end in months nor years. This war could last for decades," group spokesman Abu Firas al-Suri was quoted as having said.

"It's not a war against Nusra Front, it's a war against Islam,” he added in an audio message published on the group's social media network in its first reaction since the launch of the U.S.-led strikes on Tuesday.

The airstrikes that include some Gulf and European nations killed scores of Al-Nusra fighters in an attack on a base in a rebel held area of northwestern Syria on the first day of the military campaign, according to Reuters.

"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 said.

The United States has been carrying out strikes in Iraq since August 8 and in Syria, with the help of Arab allies, since Tuesday. It says the campaign is aimed at "degrading and destroying" Islamist terrorists who have captured swathes of both countries.

Al-Nusra Front, whose leader pledged allegiance to Al-Qaeda leader Ayman Al-Zawahiri, has been heavily involved in the fighting in Syria as well as in neighboring Lebanon, where it has claimed responsibility for several bombings and has also threatened local Sunnis.

Most recently, members of the group kidnapped 45 Fijian UN peacekeepers and threatened to try them under Islamic law before ultimately releasing them.