Poland's Prime Minister has accused Russian President Vladimir Putin of being behind a migrant crisis at Belarus's border with Poland, BBC reports.
Mateusz Morawiecki said that Belarus's authoritarian leader, a close ally of Putin, is orchestrating the crisis, but "it has its mastermind in Moscow".
At least 2,000 migrants are stuck at the border in freezing conditions.
Belarus's leader Alexander Lukashenko denies claims it is sending people over the border in revenge for EU sanctions.
Video footage shows crowds of people on the Belarusian side of a barbed-wire border fence with Poland. Some try to force their way through using bolt cutters, tree trunks and group force, while Polish guards fend them off with what appears to be tear gas.
Many of the migrants are young men but there are also women and children, mostly from the Middle East and Asia. They are camping in tents just inside Belarus, trapped between Polish guards on one side, and Belarusian guards on the other.
Overnight temperatures at the border have slumped below zero and several people have already died in recent weeks.
Speaking on Tuesday at an emergency parliamentary session after visiting troops on the border, Morawiecki said: "This attack which Lukashenko is conducting has its mastermind in Moscow, the mastermind is President Putin."
He accused the Russian and Belarusian leaders of trying to destabilise the European Union - which the two countries are not part of - by allowing migrants to travel through Belarus and enter the bloc.
Morawiecki described the situation as "a new type of war in which people are used as human shields", and said Poland was dealing with a "stage play" which is designed to create chaos in the EU.
He added that it was the first time in 30 years that Poland's border security had been so "brutally attacked".
Poland has deployed extra troops to the border, and warned of a possible "armed" escalation, fearing that Belarus might try to provoke an incident.
Poland, Lithuania and Latvia, which are all part of the EU, have seen a surge in the number of people trying to enter their countries illegally from Belarus in recent months. On Tuesday, Lithuania declared a state of emergency on its border with Belarus, which will come into effect at midnight.
Poland has seen the most arrivals, especially around its major border crossing at Kuznica.
