By Julia Symmes Cobb (Reuters) – Tensions between neighbors Venezuela and Guyana have ratcheted up in recent weeks over a long-running territorial dispute. At issue is a 160,000-square-km (62,000-square-mile) border territory around the Esequibo river, which is mostly jungle, and an offshore area where massive discoveries of oil and gas have been made. Both countries claim ownership of the territory, which is sparsely populated and whose much-disputed border was agreed under a 1899 decision when Guyana was still part of the British Empire. WHAT HAS SPARKED THE TENSIONS? Venezuela reactivated i…