Swedish chemical weapons expert Ake Sellstrom and UN disarmament chief Angela Kane arrived Wednesday from neighboring Lebanon.
The Syrian government has invited them to visit Damascus for talk on the terms of a possible UN investigation.
The Syrian regime and the rebels fighting to topple President Bashar Assad accuse each other of using chemical agents in a March 19 incident in the village of Khan al-Assal on the edge of the northern city of Aleppo.
The government has asked the UN to investigate the Khan al-Assal incident, but refused to have a possible inquiry include other alleged chemical attack sites in the central city of Homs, Damascus and elsewhere.
Syrian rebels kill woman in attack on civilian convoy, activists say
Rebels attacked a convoy of trucks and buses in northern Syria, activists said on Wednesday, after Islamist militants had warned they would target all vehicles on the road to stop the army from using its only remaining route to Aleppo
One woman was killed and 19 people were wounded, some critically, according to the Syrian Observatory for Human Rights, an anti-Assad monitoring group based in Britain.
The hardline Islamist rebel group Ahrar al-Sham uploaded video footage of the attack onto YouTube on Tuesday. It shows rebels firing artillery and mortars from a barren hillside and several trucks on fire. There is no return fire from the convoy of around 30 vehicles on the road between Salamiyeh, east of the central city of Homs, and Aleppo, Syria's largest city.
The road is the army's only route to the embattled city of Aleppo, with the rest blocked by rebels, the Observatory's director, Rami Abdelrahman, said by telephone.
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