BEIRUT -- The commander of Syria's main Western-backed rebel group has urged all opposition fighters to join ranks in the struggle against President Bashar Assad's forces, pledging to do everything he can to stave off rebel infighting.

In remarks broadcast Friday by a pan-Arab satellite television Al-Arabiya, Gen. Salim Idris said all rebels in Syria who believe in the "goals of the revolution" are "our brothers." Idris spoke after a meeting late Thursday in Istanbul with U.S. Ambassador to Syria Robert Ford.

His comments suggested he was trying to limit the damage from deadly infighting among moderate and extremist rebel factions ahead of a peace conference for Syria scheduled to be held in Switzerland in January.

The faction that Idris leads, the Supreme Military Council of the Free Syrian Army rebel umbrella group, has been dealt a severe blow by the rapid rise of Islamic extremist groups in Syria.

Earlier this month, the U.S. and Britain suspended nonlethal military aid to the opposition in Syria, after Islamic militants captured warehouses that contained a cache of machine-guns and ammunition intended for Idris' SMC.

The incident was an embarrassment to the Syrian opposition, which is struggling to maintain international support as extremists expand their hold across rebel-held territories.

"The Supreme Military Council reaffirms that it is working to secure military and relief supplies to the fighters on the ground and to ward off strife, unite ranks and assimilate all fighters on the ground who believe in the goals of the revolution of the Syrian people," Idris said.

Also Friday, the UN-Arab League's envoy to Syria, Lakhdar Brahimi, met with U.S. and Russian officials to try to agree on which nations should be invited to Syria peace talks in Geneva next month.

Disputes over who should represent the Syrian opposition and government, and whether Iran, Saudi Arabia and other regional powers should be at the table, have blocked previous attempts to bring Syria's warring sides for peace talks.

Idris has said he will take part in the Geneva talks, but it is still unclear if any other rebel groups will attend. Assad's government has said it would take part in the talks.

However, the leader of one of the most powerful al Qaeda-linked groups in Syria, Jabhat al-Nusra, said in an interview broadcast late Thursday that his group will not acknowledge anything that comes out of the peace conference.

"Geneva (conference) is an attempt to resuscitate the regime by the international community," said the man purported to be Abu Mohammad al-Golani, the Nusra Front leader, said in his first-ever interview, broadcast in full late Wednesday on the Qatar-owned Al-Jazeera television.

Al-Golani said those who plan to participate in the Geneva conference do not represent the Syrian people.

Meanwhile, a leading international human rights organization urged Lebanon to rein in sectarian tensions that have been on the rise amid a spillover of the Syrian conflict.

Human Rights Watch said Lebanese security forces need to better protect minority Alawites in the northern city of Tripoli, only 30 kilometres from the Syrian border. Alawites, a Shiite offshoot sect, have increasingly come under attack by Lebanon's Sunni extremists, who support Syrian rebels trying to topple Assad, a member of the Alawite sect.

With its own explosive sectarian mix, Lebanon has been most vulnerable to Syria's conflict, now in its third year, and has struggled to cope with a massive influx of Syrian refugees. Local Lebanese factions loyal to Syria's warring sides have often clashed along sectarian lines.

Lebanon is divided into a patchwork of sects, including Sunnis, Shiites and Christians. The country's Muslim and Christians militias bitterly fought during Lebanon's 1975-1990 civil war.

Associated Press writers John Heilprin in Geneva contributed to this report.