Two major international watchdogs allege that human rights abuses and war crimes have occurred in eastern Ukraine this year, where clashes between Russia-backed separatists and pro-Kyiv forces have killed at least 3,500 people since April.
On Monday, Amnesty International reported it has evidence that "strongly" suggests both sides carried out extra-judicial killings.
In one case, investigators found nine bodies in mass graves. Five of the dead appeared to have been pro-Russian separatists killed while fighting, while the four others were "extra-judicially executed by Kyiv-controlled forces."
Human Rights Watch also said Monday that after a week-long investigation in eastern Ukraine, it documented "widespread use" of cluster munitions in clashes between separatists and government forces.
The international watchdog said it could not determine which side used the rockets. But it added that evidence "points to Ukrainian government forces' responsibility" for several cluster bomb attacks on the separatist stronghold of Donetsk.
While the international rules of war do not ban cluster munitions explicitly, they criminalize the use of "indiscriminate" weapons deployed in a civilian area.
Russia and Ukraine are not parties to the Convention on Cluster Munitions that prohibits their use entirely.
Last month's cease-fire has mostly held in the region, except in Donetsk, where Kyiv's forces and the insurgents have engaged in daily clashes for control of the city's airport that neither side has been able to claim.
Earlier Monday, Russian Foreign Minister Sergei Lavrov criticized the sanctions imposed on Russia for its annexation of the Crimean peninsula from Ukraine and alleged support for separatists in eastern Ukraine.
In a public lecture in Moscow, Lavrov said the fact that the European Union imposed its latest sanctions on Russia after Ukraine's government and the Russia-backed separatists signed a cease-fire last month shows that the situation in Ukraine is being used, primarily by the United States, to "put Russia in its place."
Russia on Tuesday will further restrict food imports from the EU in response to those sanctions.
The country's agriculture supervisory agency announced Monday that "temporary restrictions" will go into effect on European beef and pork offal (entrails and internal organs); and beef, pork and chicken fat.