U.S. President Barack Obama has said his country is working with Russia on finalizing a ceasefire deal in Syria. Obama told a news conference alongside the G20 summit in Hangzhou that Washington still has “grave differences” with Moscow over which Syrian parties to support.

The White House says Obama and his Russian counterpart, Vladimir Putin, are likely to talk informally on the sidelines of the G20 summit. A senior U.S. state department official said earlier that a ceasefire deal could be announced as early as today.

The ongoing civil war in Syria has killed more than 250,000 people. The war also displaced 11 million civilians, causing a refugee crisis across the Middle East and Europe.