LONDON—Sanctions have nearly halved Iran’s petroleum export revenue in the past two years, OPEC data showed Friday, as the impact of international restrictions on its oil deepens. Iran has been locked in talks with six world powers to reach a final understanding over its controversial nuclear program. But despite the signature of an interim deal in November, the two sides have failed to make significant headway, leaving Iran’s economy in tatters. In its annual statistical report, the Organization of the Petroleum Exporting Countries said revenue generated by Iranian petroleum exports fell to $61.92 billion in 2013, down 46% from $114.75 billion in 2011. International sanctions banning sales of Iranian oil to the European Union and limiting them in Asia cut the country’s petroleum exports by 42% in 2013 compared with the previous year. Though oil sales had already fallen in 2012, the drop in volumes had been largely compensated […]