berlin ukrainian president petro poroshenko tell german chancellor angela merkel friday would work implement rapid exchange prisoners hold side line conflict eastern ukraine spokesman merkel say friday merkel speak telephone poroshenko friday day speak russian president vladimir putin say merkel deputy spokesman georg streiter merkel poroshenko welcome decision party recommit ceasefire agreement sign 2015 ahead christmas holiday agree lead longer-term improvement security situation region russian-backed separatist insurgency erupt 2014 bloodshed continue despite ceasefire 10,000 people kill casualties report near-daily basis poroshenko merkel underscore importance agreement party exchange prisoners call important step toward implementation minsk agreements streiter say president poroshenko stress would push ensure exchange happen soon possible add two leaders also discuss withdrawal russian officer joint center control coordination play important role support observer mission organisation security cooperation europe agree russian officer return center quickly say german french experts could get involve mediate role come days merkel also welcome poroshenko plan submit draft law set independent anti-corruption court spokesman say ukraine 's poroshenko vow work quick exchange prisoners germany