U.N. Secretary-General Ban Ki-moon is warning that any possible airstrikes against Sunni extremists in Iraq could be ineffective and backfire. He is urging Iraq's feuding communities to unite against the terrorists who have captured a vast swath of territory.

The U.N. chief urged the Iraqi government and its supporters not to retaliate against Sunni communities in revenge for "barbaric attacks" by the al-Qaida inspired extremists.

The Iraqi government has sought U.S. airstrikes to stem the insurgency by Sunni extremists but President Barack Obama has held off for now.

Ban addressed the Iraq crisis Friday in a speech to the Asia Society on Syria, saying "suddenly, the cohesion and integrity of two major countries, not just one, is in question." He called for a U.N. arms embargo on all Syrian parties.