BERLIN, June 22 - The Organization for Security and Co-operation in Europe, monitoring a fragile ceasefire in eastern Ukraine, has called on Ukraine and Russian-backed separatists to do more to investigate violations of the agreement.

Alexander Hug, deputy director of the OSCE monitoring mission in Ukraine, told Reuters that both sides often failed to investigate and take action on ceasefire violations, such as the discovery of unauthorized weapons, the downing of drones and attacks on OSCE personnel.