Venezuela on Tuesday demanded that neighboring Guyana halt oil exploration being carried out by Exxon Mobil Corp in disputed offshore territory in an escalation of a long-running border dispute between the two South American nations. Exxon last month said it found oil off Guyana's coast, spurring complaints from Caracas that Guyana is unfairly exploiting a disputed territory that must be negotiated through a mechanism created via a 1966 treaty signed in Geneva.