U.N. investigators arrived in SyriaWednesday to discuss a possible inquiry into allegations of chemical weapons usage in the Syrian conflict. Swedish chemical weapons expert Ake Sellstrom and U.N. disarmament chief Angela Kane are expected to meet with Syrian officials in Damascus to discuss about adozen casesin which there was suspected chemical weapons use.

 Syria requested an inquiry into a March 19 attack in the northern village of Khan al-Assal, but has refused access to sites of other suspected incidents. The government and opposition fighters have traded blame over the use of chemical weapons in attacks. Meanwhile, Jabhat al-Nusra fighters declared the route connecting central Syria with the northern province of Aleppo a militarized zone and warned civilians tostay off the road, threatening to target vehicles.

The Syrian regime has used the route to deliver supplies to the north since rebel fighters cut off the main highway between Damascus and Aleppo. If opposition forces succeed in blocking this only remaining route to Aleppo, it will be a major setback to the regime. On Tuesday, rebel fightersattacked a convoyof about 30 trucks and buses on the road, killing one woman and injuring 19 people, according to the British-based Syrian Observatory for Human Rights. Activists reported the victims were all civilians, while an unidentified voice in a video posted of the attack said the fighters hit a military convoy.