Ukrainian President Petro Poroshenko has tried to keep his peace plan to settle the conflict with pro-Russian separatists on track in a four-way phone call with Russian President Vladimir Putin and the leaders of France and Germany.The European Union set a Monday deadline for Russia and the separatists to take a series of steps. If this was not done, the EU warned that it was ready to impose new punitive measures on Russia.A statement released by Poroshenko's office said he underlined Ukraine's willingness to maintain a cease-fire at least until Monday evening, but expressed concern about the situation, noting what he said were multiple violations of the cease-fire by separatist fighters.Poroshenko's discussion Sunday with Putin, German Chancellor Angela Merkel and French President Francois Hollande was the latest in a series they have held in recent weeks in an effort to stop the fighting that has killed more than 400 people since April.