WARSAW—Poland will buy 250 U.S. tanks as part of a deal worth around $6 billion, the defense minister said on Wednesday, as the NATO member seeks to bolster its defenses. In common with many other eastern European countries, Poland has been unnerved by what it sees as increased Russian assertiveness since Moscow annexed Crimea from Ukraine in 2014. “Of course this is a response to the challenges we face in terms of international security,” Mariusz Blaszczak told a news conference. “Our task is to deter a potential aggressor. We all know where that aggressor is.” Blaszczak said Poland would spend 23.3 billion zlotys ($6 billion) on the Abrams tanks and an accompanying logistical and training package, as well as on upgrading infrastructure and buying ammunition. In May, Poland announced that it would buy 24 armed drones from Turkey, becoming the first NATO member to buy Turkish-made unmanned aerial vehicles (UAVs). …