MOSCOW (Reuters) - Police in Belarus detained 313 people on Sunday during protests in which thousands marched through Minsk calling for President Alexander Lukashenko to step down, the Belarusian Interior Ministry said. Belarus has been in a political crisis since a presidential election in August that the opposition says was rigged. The authorities deny vote fraud. Reporting by Maxim Rodionov; writing by Tom Balmforth; Editing by Kevin Liffey