President Bashar al-Assad, meanwhile, said he was "very confident" of victory in Syria's conflict and threatened Israel with retaliation for any attack, in an interview aired late yesterday.
In Istanbul, the deeply divided opposition announced agreement on expanding its membership to include more representatives of fighters and activists on the ground after it was accused of being out of touch.
But despite extending its talks for five days longer than scheduled, the National Coalition put off until June electing a new leader and forming an interim rebel government.
"There is a world war being waged against Syria and the policy of (anti-Israeli) resistance... (but) we are very confident of victory," he told Hezbollah's Al-Manar television.
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Syrian state television said troops and Hezbollah fighters had captured the Arjun district in northern Qusayr yesterday, leaving rebels holed up in the town little chance to escape.
Qusayr controls supply routes vital to both sides and access between Damascus and the Mediterranean.
"Around 1,000 fighters from across Syria" have penetrated the rebel stronghold near the Lebanese border, the National Coalition's interim leader George Sabra told reporters in Istanbul.
"Hundreds" of rebels have broken through army lines near the village of Shamsinn, northeast of Qusayr, after losing 11 fighters, according to Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
The Coalition has appealed for the rescue of 1,000 civilians wounded in Qusayr, which Assad's forces have been trying to seize back in an all-out offensive since May 19.
"There is clear popular pressure to open a new front of resistance in the Golan," he said, echoing a call from Hezbollah's leader Hassan Nasrallah.
"There are several factors, including repeated Israeli aggression," he added of reported Israeli air strikes on Syria and said, "We have informed all the parties who have contacted us that we will respond to any Israeli aggression next time.