The U.N. political chief says deadly rocket attacks on the Ukrainian port city of Mariupol this weekend that "knowingly targeted civilians" violated international humanitarian law and could amount to war crimes.

Jeffrey Feltman told an emergency meeting of the U.N. Security Council Monday that monitors from the Organization for Security and Cooperation in Europe who examined the craters reported that the rockets originated from territory controlled by pro-Russian rebels.

He said Saturday's attack on Mariupol — a strategic city that could provide a land corridor into Ukraine's Crimean peninsula which Russia annexed last March — destroyed buildings and hit a market killing dozens of people, including women and children, and injuring over 100. Other reports put the death toll at 30.

Feltman said the perpetrators must be brought to justice.