BEIRUT, Lebanon — The Syrian government and Syrian rebels traded accusations about a lethal attack in the northern province of Aleppo on Tuesday, in which each side in the country’s two-year-old conflict said the other had used chemical weapons.

But neither side presented clear documentation, and two American officials said there was no evidence to suggest that any chemical weapons had been used. A Defense Department official said the claim should be treated with caution, if not outright skepticism.

The first report came from the Syrian state news agency, SANA, which reported that terrorists, its term for armed rebels, had fired a rocket “containing chemical materials” into the Khan al-Assal area of Aleppo Province, killing 16 people and wounding 86. It later raised the death toll to 25.

The news agency displayed photographs of what it said were the victims, but there was no indication in the photographs that they had suffered a chemical attack, like burns or skin discoloration or quarantine measures.