"The Belarusian defence ministry considers the accusations of the Polish side unfounded and unsubstantiated," it said in a statement.

Poland on Monday said it had blocked a bid by hundreds of migrants to enter the country from Belarus and warned of an "armed" escalation with thousands more massed near the border.

Washington and Brussels called on Minsk to stop what they described as an orchestrated influx and Polish Prime Minister Mateusz Morawiecki said Tuesday the border crisis threatens the security of the entire European Union.

The Belarusian defence ministry Tuesday in turn accused Poland of "deliberately" escalating tensions.

It said Poland had deployed 10,000 military personnel to the border without giving prior warning to Belarusian authorities, in what it said was a violation of joint security agreements.

Minsk said that according to the agreements, observers should be present at any deployment of more than 6,000 military personnel.

"Minsk has so far not received any notification or invitation of observers from the Polish side."

Belarusian interior minister Ivan Kubrakov told the state-run news agency Belta earlier Tuesday that the migrants were in the ex-Soviet country "legally," adding: "there have been no violations of the law on the part of migrants so far."