President of European Council says leaders must remain united

European leaders have been told they must remain united, in the face of challenges facing the EU.

The call came from President of the European Council Donald Tusk at a ceremony to mark the 60th anniversary of the Treaty of Rome.

The Taoiseach Enda Kenny was among 27 leaders who attended - however British Prime Minister Theresa May wasn't there.

She's due to start the Brexit process on Wednesday.

Donald Tusk says European unity is not just an optional extra: