Polish Foreign Minister Radoslaw Sikorski is warning Western countries that Russia could expand its military aggression in Ukraine to other countries. If Russian President Vladimir Putin and former Russian President Dmitry Medvedev make threats, then unfortunately he has to believe them, the liberal-conservative politician said in comments carried by broadcaster TVN24 on Sunday. It was necessary to prepare for the fact that Russia could put NATO’s security guarantees to the test, Sikorski said. Poland has been a member of the transatlantic defence alliance since 1999. The pro-Russian prime min…