Supporters of Venezuela's opposition (R) face riot police officers who are blocking a street, as they take part in a rally to demand a referendum to remove Venezuela's President Nicolas Maduro, in Caracas, Venezuela, September 16, 2016. REUTERS/Stringer FOR EDITORIAL USE ONLY. NO RESALES. NO ARCHIVES.

People wait to buy staple items and basic food outside a supermarket in Caracas, Venezuela September 14, 2016. REUTERS/Henry Romero

Supporters of Venezuela's opposition face police officers who are blocking a street, as they take part in a rally to demand a referendum to remove Venezuela's President Nicolas Maduro, in Caracas, Venezuela, September 16, 2016. REUTERS/Henry Romero

Lilian Tintori (C), wife of jailed Venezuelan opposition leader Leopoldo Lopez takes part in a rally to demand a referendum to remove Venezuela's President Nicolas Maduro, in Caracas, Venezuela, September 16, 2016. REUTERS/Henry Romero

(L-R) Ireland's Prime Minister Enda Kenny, Cyprus' President Nicos Anastasiades , Denmark's Prime Minister Lars Lokke Rasmussen, Germany's Chancellor Angela Merkel, Belgian Prime Minister Charles Michel and Italy?s Prime Minister Matteo Renzi attend the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Yves Herman

European Union leaders pose for a family photo during the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Leonhard Foeger

Hungary's Prime Minister Victor Orban (L), Germany's Chancellor Angela Merkel and Austria's Chancellor Christian Kern (R) arrive to pose for a family photo during the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Leonhard Foeger

European Parliament President Martin Schulz (L) is welcomed by Slovakia's Prime Minister Robert Fico at the Government office ahead of the upcoming European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 15, 2016. REUTERS/Yves Herman