KYIV (Reuters) - Nearly nine hours of talks between Ukraine and Russia on Thursday failed to produce a breakthrough on signing a joint document, but both sides agreed to keep talking, the chief of staff to Ukraine's president said after the talks in Berlin.

       Ukrainian and Russian officials met in the German capital for talks on ending the conflict in eastern Ukraine, with tensions running higher after Russia massed more than 100,000 troops near Ukraine's borders in recent weeks.

       Andriy Yermak, the chief of staff to President Volodymyr Zelenskiy, told a televised briefing that both sides would likely meet again soon and hoped for a breakthrough on prisoner exchanges and the opening of checkpoints in eastern Ukraine.

       (Reporting by Natalia Zinets and Matthias Williams; Editing by Leslie Adler)