WARSAW, Feb 9 (Reuters) - Poland will close a key border crossing with Belarus until further notice, the Polish interior minister said on Thursday, as relations between Warsaw and Minsk sink to new lows. The already tense ties between Poland and Belarus were further strained on Wednesday when a journalist of Polish origin was sentenced to eight years in prison by a Belarusian court in a trial Warsaw says was politically motivated. See here for a complete list of exchanges and delays