The head of Syria's al Qaeda-linked Nusra Front has said US-led air strikes will not defeat Islamists in Syria and warned that militants might launch retaliatory attacks against Western countries.Abu Mohamad al-Golani, in an audio message posted on pro-Nusra jihadi forums, urged European and US citizens to denounce the US actions if they wanted to keep out of the war."Muslims will not watch while their sons are bombed. Your leaders will not be the only ones who would pay the price of the war. You will pay the heaviest price," he said, warning that the battle would be brought "to the hearts of your homes"."You should protect yourselves from this war by standing against the decisions of your rulers and stop them from bringing you the woes (of war)," he said.The United States has been carrying out strikes against Islamic State fighters in Iraq since Aug. 8. It opened a new front on Sept. 23, attacking militants in neighboring Syria.Washington says the campaign, backed to varying degrees by Arab and Western allies, is aimed at "degrading and destroying" militants who have captured swathes of both Iraq and Syria.Islamic State and the Nusra Front share the same ideology and rigid Islamic beliefs, but they fell out during a power struggle and have been battling each other this past year.Nusra Front is now coming under pressure from its own members to reconcile with Islamic State and join forces to fight what they describe as a "crusader" campaign against Islam.At least 50 fighters from the Nusra Front were killed in the first wave of US-led attacks in Syria last Tuesday, a British-based monitoring group said.