International mediator Lakhdar Brahimi says Syria's civil war could spread across Middle Eastern borders into an “all-consuming conflict” unless the violence is eventually contained.

Brahimi, speaking Wednesday after talks in neighboring Lebanon, called on Syrian President Bashar al-Assad's government to take the lead in implementing a proposed cease-fire during the Muslim holiday of Eid al-Adha, which begins next week. He said if the government takes the first step, Syria's opposition had told him they would reciprocate immediately.

The U.N.-Arab League envoy for Syria has visited Sunni Muslim states that support anti-government rebels as well as Shi'ite Iran, Mr. Assad's strongest regional ally, in his search for a political solution to Syria's 19-month conflict.

Brahimi met Wednesday with Lebanese President Michel Suleiman, Prime Minister Najib Mikati and the country's parliament speaker. On Sunday, the international envoy appealed to Iranian leaders to support the proposed Syrian cease-fire.

A truce brokered by Brahimi's predecessor, former U.N. chief Kofi Annan, fell apart shortly after it took effect in April.

The fighting continued Wednesday. Rights groups said rebels shot down a Syrian military helicopter as troops fought to retake the northwestern town of Maaret al-Numan along the Damascus-Aleppo highway.