The United States has said it will refuse visas to foreign officials who block Americans’ social media posts, as Donald Trump’s administration wages a new battle over free expression. Marco Rubio – the secretary of state who has controversially rescinded visas for activists who criticize Israel and ramped up screening of foreign students’ social media – said on Wednesday he was acting against “flagrant censorship actions” overseas against US tech firms. He did not publicly name any official who would be denied a visa under the new policy. But last week he suggested to lawmakers that he was planning sanctions...