Lakhdar Brahimi, the UN-Arab League joint envoy, has called for talks between the Syrian opposition and an "acceptable delegation" from the Damascus government on a political solution to the country's 23-month-old civil war.
In a joint press conference in Cairo with Nabil El-Araby, the Arab League secretary-general, Brahimi said on Sunday that negotiations could begin on UN premises. He gave no specific location.
The initiative of opposition leader Mouaz al-Khatib, which calls for talks with any Syrian representative not directly involved in repression, "has opened the door and challenged the Syrian government to live up to what it has been continuously saying, that it is ready for dialogue and a peaceful solution", Brahimi said.
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Khatib, the head of the Syrian National Coalition, offered last week to hold talks with President Bashar al-Assad's ceremonial deputy, Farouq al-Sharaa, on a political transition in which Assad would be given safe passage to go into exile.
"We believe that if a dialogue begins at the offices of the UN, at least at the start, between the opposition and an acceptable delegation from the Syrian government, we think this will be a start to get out of the dark tunnel," Brahimi said.
It was unclear whether he had received any indication of Syria's willingness to enter into talks with Khatib and his bloc.
Meanwhile, El-Araby said he will travel to Russia, one of Assad's main foreign allies, on Tuesday for talks with envoys of four Arab states. Syrian Foreign Minister Walid al-Muallem is also due to visit Moscow later this month.
Brahimi confirmed that Khatib would himself visit Moscow next month, adding that he had discussed that trip with El-Araby.
In another development, the National Coalition accused members of Lebanon's Shia group Hezbollah of intervening in the conflict in Syria.
Hezbollah fighters crossed into Homs province on Saturday and attacked "three Syrian villages in the Qusayr region near the Lebanese border," the coalition said.
The operation resulted in "civilian casualties and the exodus of hundreds of people," and it has also "stoked sectarian tensions" in the area, the opposition said.
In Lebanon, a Hezbollah official said three Lebanese Shias were killed in clashes in Syria while acting in "self-defence", without specifying if they were Hezbollah members.
Elsewhere in Syria, fierce clashes raged on Sunday between government troops and several rebel battalions in Aleppo, with fighters seizing an army checkpoint near Nayrab military airbase, activists said.
Nayrab is adjacent to Aleppo international airport, a key target for the rebels who have also been battling troops guarding Kwiyres military airbase east of the city and Menegh airbase to the north.