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.
"We are discussing with Latvia, and especially with Lithuania, whether to trigger Article 4 of the NATO treaty," Mateusz Morawiecki told Polish state-run news agency PAP.
"It is not enough just for us to publicly express our concern - now we need concrete steps and the commitment of the entire alliance."
Thousands of migrants have travelled 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 it has imposed, but Belarus has repeatedly denied this. Some countries in the region have warned the stand-off could escalate into a military conflict.
Russian President Vladimir Putin, a key backer of Belarus leader Alexander Lukashenko, said that Russia was ready to help resolve the crisis, RIA news agency reported on Sunday, citing an interview on a state TV channel.
Morawiecki told PAP that EU leaders would discuss further sanctions against Belarus. "We will certainly discuss further sanctions, including the complete closure of the border," he was quoted as saying.
He also said that the EU should jointly finance the construction of a border wall.
Meanwhile, Polish forces described an increasingly tense situation on the frontier, with the Border Guard saying it expected another "big attempt" to break through.
On Saturday, a group of about 50 migrants broke through defences on the border and entered Poland near the village of Starzyna, police said on Sunday.
All of the people were caught by Polish uniformed services and brought back to the border, Border Guard spokeswoman Katarzyna Zdanowicz told Polish state news agency PAP.
The police also said an officer was admitted to hospital after being hit with a stone.
The spokesman for Poland's security services Stanislaw Zaryn wrote on Twitter on Sunday about reports of trucks carrying stones and rubble from Belarusian construction companies to areas near the border.