Venezuela has for decades claimed two-thirds of Guyana's territory as its own, arguing that the gold-rich region west of the Essequibo River was stolen from it by an 1899 agreement with Britain and its then colony.
The area is a fixture of 19th century maps of Gran Colombia, the short-lived republic revered by the late Venezuelan leader Hugo Chavez.
Ties between the two countries had improved recently. Chavez's successor, Nicolas Maduro, made his first visit as president to Georgetown in August to discuss joint oil projects with his Guyanese counterpart, Donald Ramotar. During the visit, Maduro described the dispute as a relic of the colonial era and vowed to peacefully resolve the issue.