Newly re-elected Cameron will use a summit in the Latvian capital between the EU and six former Soviet republics on Friday to sound out other EU leaders on his demands for changes before a British referendum on EU membership that he has promised before the end of 2017.

Cameron has not arranged formal meetings with Merkel and Hollande, among the EU's most influential leaders, in Riga but he will probably have a chance to speak to them on the sidelines of the meeting, the British official said.

(Reporting by Kylie Maclellan, editing by Adrian Croft)