BEIRUT, Lebanon — The Syrian government and Syrian rebels traded accusations about an attack in the northern province of Aleppo on Tuesday, in which each side in the country’s two-year 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” on Tuesday into the Khan al-Assal area of Aleppo province, killing 16 people and wounding 86. It later raised the death toll to 25.