"A meeting of the Tripartite Liaison Group should take place as soon as possible so that a ceasefire will be established on December 9," he wrote.

Earlier, Poroshenko said representatives of Ukraine, Russia and the OSCE would told a meeting of the tripartite contact group on December 9.

However, Donetsk militant leader Denis Pushilin told reporters on Sunday that the militants would be ready to hold talks no earlier than December 12, according to the Interfax news agency.