International envoy Lakhdar Brahimi is making a fresh appeal for Syria's divided opposition to attend a proposed peace conference.
Speaking in Damascus Friday, Brahimi said it would be impossible for the long-delayed Geneva talks to take place without rebel participation.
"The Syrian government ensured its participation in the conference. The opposition, whether the coalition or other parties, are still seeking a way to be presented in the Geneva conference."
Rebels have demanded President Bashar al-Assad resign before they attend the peace conference, tentatively scheduled for later this month. Brahimi says he hopes the issue can be resolved in the next few days.
Syria's main rebel bloc, the National Coalition, meets next week to decide its position on the talks. Some Islamist rebels, who reject the bloc's leadership, warn they will view any participants as traitors.
Brahimi also stressed it is the U.N. position that Iran, a key Assad supporter, attend the conference.
Meanwhile, Israeli warplanes were reported to have attacked a shipment of missiles at a Syrian military base near the port city of Latakia. Speaking anonymously Thursday, U.S. officials Thursday said the target of the Israeli airstrike was likely Russian missiles headed for the Islamic militant group Hezbollah.
The Lebanon-based Shi'ite group has been fighting alongside the Syrian government in its civil war against mainly Sunni Muslim rebels. It also fights the Jewish state.
Neither Israeli nor Syrian officials have confirmed the attack on the Syrian air base, which was hit late Wednesday or early Thursday. It is not clear if the strike succeeded in destroying the missiles.
Israel has reportedly attacked Russian or Iranian missile shipments inside Syria at least two other times this year, though it has not confirmed these attacks publicly.
Syria strongly protests the Israeli military intervention, but has so far failed to follow through on its threats of retaliation.