Illegal weapons such as cluster bombs have been used in the Ukraine conflict, Amnesty International said while also criticizing both sides in the fighting for the high number of civilian deaths.

"Taking into account everything we understand for now, we think that they (cluster bombs) were used by both sides," the organization's senior director for research, Anna Neistat told reporters in Moscow on Wednesday, adding it was difficult to determine.

In its annual report released Wednesday, Amnesty International also said both sides in the conflict are to blame for the high number of civilian deaths stemming from the indiscriminate firing of unguided mortars and rockets in populated areas.

Nearly 5,800 people have been killed since the fighting between Russia-backed separatists and Ukrainian troops began in April.

In eastern Ukraine "both sides failed to take reasonable precautions to protect civilians, in violation of the laws of war," Amnesty International said.

The group has also recorded abductions, torture and summary killings by volunteer battalions on the government side and by units fighting with the separatists, Neistat said.

Under a fragile peace deal reached on Feb. 12, both sides are required to pull back heavy weapons between 25 and 70 kilometers (15 to 45 miles) from the front line, depending on their caliber. The Ukrainian military said Tuesday that its forces would not withdraw their weapons until a cease-fire takes hold.