The Brazilian government is likely to move the dates of Rio+20, as a clash with the UK Royal Jubilee threatens to keep leaders away.
The Rio+20 summit, seen as a chance to put the global economy on a sustainable track, is scheduled for 4-6 June 2012, co-inciding with the Diamond Jubilee.
That jeopardises the attendance of leaders from 54 Commonwealth nations.
Commonwealth and G20 governments have asked Brazil to solve the problem, and a two-week postponement is now likely.
The Brazilian government will confirm the proposed new dates of 20-22 June by the end of November.
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