(AP PHOTO)Cubans have been plunged into darkness again. (AP PHOTO) Credit: AAPCuba's national electricity grid collapsed late on Sunday, the state-owned national electric utility said, plunging the island of about 10 million people into darkness as blackouts are becoming ever more frequent. Venezuela had long been Cuba's primary oil supplier, with imports from Mexico also halted amid increased US pressure. The power crisis coincides with a cautious opening of Cuba's tightly controlled energy sector, driven by fuel shortages and severe US sanctions. Havana recently authorised its first foreign-backed fuel import venture and allowed nearly 200 Cuban businesses to participate in wholesale fuel distribution.