Moscow - Ukraine's President Petro Poroshenko rejected a peace plan proposed to him last week by his Russian counterpart Vladimir Putin, Putin's spokesperson Dmitry Peskov said on Sunday evening, according to Russian media.Peskov said the plan, contained in a letter sent by Putin on Thursday evening, proposed a ceasefire by both government forces and separatist militiamen in southeastern Ukraine, as well as the withdrawal of heavy artillery by both sides."In recent days, Russia has consistently undertaken efforts as an intermediary in regulating the conflict," Peskov said in comments quoted by the ITAR TASS news agency."In particular, on Thursday night a written address was sent by the president of Russia to the president of Ukraine, in which a concrete plan was proposed to both sides in the conflict to withdraw heavy artillery."A copy of the letter was published by the Russian television channel NTV. In it, Putin proposed "urgent measures for the cessation of mutual shelling, and also the rapid withdrawal by the sides in the conflict of means of destruction with a calibre higher than 100 mm".