Further, in a report released late Monday, Human Rights Watch says the rebels have most likely used cluster weapons in the conflict as well, a detail that The New York Times could not independently verify.

The army’s use of cluster munitions, which shower small bomblets around a large area, could also add credibility to Moscow’s version of the conflict, which is that the Ukrainian national government is engaged in a punitive war against its own citizens. The two October strikes occurred nearly a month after President Petro O. Poroshenko of Ukraine signed a cease-fire agreement with rebel representatives.

“It’s pretty clear that cluster munitions are being used indiscriminately in populated areas, particularly in attacks in early October in Donetsk city,” said Mark Hiznay, senior arms researcher at Human Rights Watch, in emailed comments after the report was completed. “The military logic behind these attacks is not apparent, and these attacks should stop, because they put too many civilians at risk.”

Press officers for the Ukrainian military denied that their troops had used cluster weapons during the conflict and said that the rocket strikes against Donetsk in early October should be investigated once it was safe to do so. They also said that rebels in the area had access to powerful rocket systems from Russia that could fire cluster munitions.

However, munition fragments found in and around Donetsk and interviews with witnesses indicate that the cluster munitions that struck Oct. 2 and Oct. 5 were most likely fired by Ukrainian troops stationed southwest of the city, according to Human Rights Watch and a review by The Times. Witnesses there reported seeing rocket launches from those troops’ positions toward the city at times that coincide with the strikes.