The Fields medal was stolen from Caucher Birkar, one of the four joint winners of the award commonly called the “Nobel Prize of Mathematics”.

In a statement, the International Congress of Mathematics, which organises the award, said it “profoundly regrets the disappearance”.

The medal was being kept in Birkar’s briefcase, which was stolen and later recovered without the medal.

Police in Rio, where the awards ceremony was held, are continuing to make inquiries.