European Union sanctions are “slowly but surely” choking Russia’s oil exports -- and are also stepping up in speed and scope, according to the 27-nation bloc’s chief sanctions official. EU Sanctions Envoy David O’Sullivan told RFE/RL in an interview on December 16 that while enforcement was “a game of cat and mouse,” the measures were working and Russia’s revenues were “suffering.” O’Sullivan spoke in a video call from Brussels two days before an EU summit that’s due to consider…