The Trump administration said it was optimistic about the possibility of a ceasefire in the Ukraine conflict even as President Vladimir Putin appeared to reject US calls for immediate halt to the violence.

Russia struck a sedate tone on Friday but acknowledged grounds for cautious optimism, after only backing the "idea" of a U.S. brokered 30-day ceasefire with firm caveats.

Former Philippine President Rodrigo Duterte said he takes full responsibility for his administration's "war on drugs", in a video message posted on his Facebook account, as he braces for a legal battle at the International Criminal Court.