Kiev - A leader of pro-Russian separatists in east Ukraine, Alexander Zakharchenko, was quoted by Russia’s RIA news agency as saying rebels had launched an attack on the port city of Mariupol on Saturday. “Today an offensive was launched on Mariupol. This will be the best possible monument to all our dead,” he was quoted as saying at a memorial ceremony in the rebel-held city of Donetsk. At least 20 people were killed by shelling in Mariupol on Saturday, regional police said, in an attack Kiev blamed on the Russian-backed separatists. Russian news agency Interfax earlier said rebels had denied the attack.