Countries across the world must agree rules to share water resources or risk political and humanitarian crises, according to ex-Russian leader Mikhail Gorbachev.

The Nobel Peace Prize laureate said at the 6th World Water Forum in Marseille, France that governments must ratify the 1997 United Nations Watercourses Convention.

It is the only global legal framework to govern and manage the world’s 276 cross-border watercourses. Thirty-five countries must ratify it for it to come into force. So far, 24 countries have done so, including most recently Burkina Faso, Morocco and France, according to the charity Green Cross International which Mr Gorbachev founded.

Mr Gorbachev said: “Water is the basis for all development and its strategic importance has demonstrated it can serve as a vehicle for peace and also tension. The risk of competition between regions and countries may only increase if we do not find a way to protect and share water. A global legal instrument would help ensure equitable and sustainable management of international watercourses.”