The Ministry of Defence (MoD) has said a "small team" of armed forces personnel have been deployed to Poland "to address the ongoing situation at the Belarus border".
In a statement, the MoD said that a history of friendship is the reason they are sending troops.
The PA news agency understands that the deployment is limited to providing engineering support.
"The UK and Poland have a long history of friendship and are Nato allies," the statement read.
"A small team of UK armed forces personnel have deployed following an agreement with the Polish government to explore how we can provide engineering support to address the ongoing situation at the Belarus border."
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The statement comes amid tensions over an influx of migrants at the border between Poland and Belarus.
Migrants from the Middle East, Afghanistan and Africa previously trapped in Belarus were part of the 2,000-strong crowd making multiple attempts to force their way into Poland overnight, Warsaw said.
In response, Poland announced it had reinforced its border with extra guards.
The EU accuses Minsk of luring migrants from war-torn and impoverished countries to push them into Poland in an attempt to sow violent clashes on the bloc's eastern flank.
UN human rights chief Michelle Bachelet called on states to de-escalate and resolve the "intolerable" crisis.
"These hundreds of men, women and children must not be forced to spend another night in freezing weather without adequate shelter, food, water and medical care," she said.
"We are facing a brutal hybrid attack on our EU borders. Belarus is weapon migrants' distress in a cynical and shocking way," EU Council President Charles Michel said.
The bloc's 27 ambassadors agreed this constituted a legal basis for further sanctions, which could come as early as next week and target some 30 individuals and entities including the Belarusian foreign minister and the national airline.
"Very rapidly at the beginning of next week there will be a widening of the sanctions against Belarus," European Commission President Ursula von der Leyen told reporters after a meeting with U.S. President Joe Biden in Washington.
"We will look into the possibility of sanctioning those airlines who facilitate human trafficking towards Minsk and then the EU-Belarus border," she added.
Belarusian President Alexander Lukashenko and Russian President Vladimir Putin have pinned the blame on the EU.
The Kremlin accused Europe of failing to live up to its own humanitarian ideals and trying to "strangle" Belarus with plans to close part of the frontier.
Moscow said it was unacceptable for the EU to impose sanctions on Belarus over the crisis.
