Other lower level meetings planned for this week underscore the massive task ahead for European allies as they weigh plans for sending a peacekeeping force to Ukraine.

Oil prices were little changed on Wednesday as investors await the next steps in talks to end Russia's invasion of Ukraine, leaving in place sanctions on Russian crude and the chance of further restrictions on its buyers.

Donald Trump has signalled his support for a package of security guarantees for Ukraine, including foreign boots on Ukrainian soil from around 10 European countries, in a new push to pressure Russian president Vladimir Putin into ending the conflict.