This July 27, 2011, file image from a Web posting by al-Qaida's media arm, as-Sahab, provided by IntelCenter, shows Ayman al-Zawahiri. (Anonymous/AP)

Al-Qaeda leader Ayman al-Zawahiri has charged warring Islamist factions in the Syrian opposition with “hostile sedition” and has appealed to them to submit their differences to an arbitration council under Islamic law.

In an audio message released to jihadist forums Thursday by al-Qaeda’s media arm, Zawahiri called on the factions “to stop the fighting between the brothers of jihad and Islam immediately,” to form a commission to resolve their differences and to establish “a mechanism to compel everyone to abide” by the panel’s rulings.

The message, recorded last week, comes as the Islamic State of Iraq and Syria (ISIS), the main al-Qaeda-allied group of rebel fighters in Syria, has waged fierce battles against other extremist organizations and the so-called moderate opposition fighters backed by the United States.

The infighting and the relative strength of ISIS have undercut U.S. and other international efforts to promote the moderate groups as a viable, democratic alternative to Syrian President Bashar al-Assad.

The prominence of the Islamist extremists, who receive arms and funding from Arab states of the Persian Gulf, has also buttressed Assad’s claims that his government is under siege from terrorists rather than political opponents of his brutal 13-year rule.

At Wednesday’s opening session of United Nations-hosted peace talks in Switzerland, Syrian Foreign Minister Walid al-Moualem accused Arab neighbors of sowing terrorism and insurrection, and he charged the United States and others with interfering with Syria’s sovereign right to defend itself.

“We have come here to put an end to terrorism and its bitter consequences,” Moualem said. “Diplomacy and terrorism cannot go in parallel. Diplomacy must succeed by fighting terrorism.”

Islamist extremist groups have grown rapidly in Syria and in recent months have vied for supremacy among themselves, even as they fight Assad’s forces. ISIS, in particular, has been charged with provoking the infighting by attacking groups and employing brutal tactics against civilians.

Last month, leaders of both ISIS and another extremist group, Jabhat al-Nusra, separately appealed for an end to the internecine battles.

But the call from Zawahiri, translated from Arabic and released by the SITE Intelligence Group, reflects growing concern that the internal fighting is undermining what al-Qaeda views as a major opportunity to reestablish a permanent presence in the region, according to Andrew J. Tabler, a senior fellow and Syria expert at the Washington Institute for Near East Policy.

“The problem is that the tactics of ISIS were so harsh, it set off the fighting” among the groups, Tabler said. “It’s interesting that this also comes at a time when the issue of the extremists was front and center” at the peace talks.

“Everyone is now posturing,” he said. “Everyone is trying to look reasonable, and I think this is an attempt to do that.”

In his message, Zawahiri admonished jihadists that “your unity, association and gathering is more important . . . to us than any organizational link.” He called on them to line up “in one rowlike, solid structure in confronting your sectarian, secularist enemy,” which he identified as the Syrian government supported by “Iran, Russia and China.”

“What made our hearts bleed . . . is the hostile sedition, which has intensified among the ranks of the mujahideen of Islam,” he said, according to the SITE translation. “Therefore, we call all our brothers in all the jihadi groups . . . to seek to stop this sedition, which no one knows but Allah with what it will end.”