WARSAW (Reuters) - Belarusian soldiers threatened to open fire on Polish troops just across the border, the Polish Defence Ministry said on Thursday, in what it said was an attempt to escalate a crisis over migrants at their common frontier.

       Warsaw and the European Union accuse Belarus of deliberately encouraging illegal migrants to enter Poland and other EU states via Belarusian territory as a means to put pressure on the bloc. Belarus has repeatedly denied this.

       Poland has declared a state of emergency in the border region. It has put up a barbed wire fence on the border and plans to build a wall.

       "Yesterday... Polish soldiers located a group of around 250 migrants near the fence," the Polish Defence Ministry said on Twitter. "The Belarusian soldiers guarding them, threatened to open fire at our soldiers."

       The Polish soldiers "did not allow themselves to be provoked" and as a result the situation did not escalate further, the ministry added.

       The Belarusian foreign ministry did not immediately respond to a request for comment.

       The European Commission and Warsaw say the flow of migrants has been orchestrated by Belarus as a tactic designed to pressure the EU over sanctions it imposed on Minsk. President Alexander Lukashenko is no longer recognised by the EU as legitimate head of state.

       On Wednesday, Poland accused Belarus of staging an armed cross-border intrusion and said it had summoned the Belarusian charge d'affaires to protest over what it said was "a deliberate escalation" of the migrant crisis.

       Belarus denied that such an intrusion took place.

       "Warsaw's systemic attempts to groundlessly and shockingly raise the level of tension on the Belarusian-Polish border are seriously alarming," the Belarusian foreign ministry said on its website, calling the accusation unfounded.

       (Reporting by Alan Charlish in Warsaw and Matthias Williams in Kyiv; Editing by Frances Kerry)