HAJNOWKA, Poland—NATO must take “concrete steps” to resolve the migrant crisis on the Belarus border, the Polish prime minister was quoted as saying on Sunday, adding that Poland, Lithuania, and Latvia may ask for consultations under Article 4 of the alliance’s treaty. Under Article 4, any ally can request consultations whenever, in the opinion of any of them, their territorial integrity, political independence, or security is threatened. “It is not enough just for us to publicly express our concern—now we need concrete steps and the commitment of the entire alliance,” Mateusz Morawiecki told Polish state-run news agency PAP. Thousands of migrants have traveled to Belarus in the hope of crossing into the European Union (EU), only to find themselves trapped on the border in freezing conditions. The EU accuses Minsk of orchestrating the crisis to put pressure on the bloc over sanctions, but Belarus has repeatedly denied this. Some countries …