DAMASCUS, Syria (AP) — Syria's government and rebels traded accusations Tuesday of a chemical attack on a northern village for the first time in the civil war, although the U.S. said there was no evidence it had happened.

The use of such weapons would be a nightmare scenario in the 2-year-old conflict that has killed an estimated 70,000 people, and the competing claims showed awillingness by both sides to go to new levels to seek support from world powers.

One of the international community's biggest concerns is that Syria's arsenal of chemical weapons could be used by one side or the other, or could fall into the hands of foreign jihadi fighters among the rebels or the Lebanese militant group Hezbollah, which is allied with the regime of President Bashar Assad.