EU chief Ursula von der Leyen said Sunday "the devil is always in the details" as she spoke of a budding South America trade deal that France has vowed to block at all costs.

Von der Leyen, speaking to Brazil's Globo News on the eve of a G20 summit she is attending in Rio de Janeiro, admitted that her European Commission faced "a big task" in getting member countries of the EU and South America's Mercosur bloc on board.