The leaders of France, Germany and Russia have spoken by phone and are exploring the possibility of a summit with Ukraine's president about the conflict in the country's east.

French President Francois Hollande's office said he, German Chancellor Angela Merkel and Russian President Vladimir Putin agreed Saturday that a summit in the coming weeks "could prove useful." The leaders welcomed new efforts toward an effective cease-fire in eastern Ukraine.

The warring sides have called for a cease-fire Sept. 1.

Merkel and Hollande have held several four-way conversations with Putin and Ukrainian President Petro Poroshenko.

The German government said the three leaders speaking Saturday underlined their readiness to keep working in that format, but didn't mention a summit. Kremlin said "preparations for a new meeting at the highest level" were discussed.