Ecuador has reportedly given the US military permission to use a Galapagos island as an airfield, angering critics in the South American country who say the agreement is unconstitutional.

Under an apparent deal - denied by the US - with Ecuador's right-wing government, the Pentagon will use the tiny airport on San Cristobal island to "fight drug trafficking", defence minister Oswaldo Jarrin said.

A US air force Boeing 707 plane carrying radar surveillance and a Lockheed P-3 Orion plane will patrol the Pacific Ocean, using the Galapagos as a launching off point, Latin American TV network Telesur reported.

But according to Ecuador's 2008 constitution, "the establishment of foreign military bases or foreign installations for military purposes will not be allowed".