A "small team" of British military engineers have deployed to the Polish border with Belarus amid rising tensions between the neighbouring countries.
The personnel will explore ways in which engineering support can be provided to Poland as a huge number of migrants gather on the Belarusian side of the border.
A Ministry of Defence spokesperson said: "The UK and Poland have a long history of friendship and are NATO allies.
"A small team of UK Armed Forces personnel have deployed following agreement with the Polish Government to explore how we can provide engineering support to address the ongoing situation at the Belarus border."
The deployment of the British military personnel will be limited to engineering support.
The European Union has accused Belarus' authoritarian president, Alexander Lukashenko, of encouraging illegal border crossings as a "hybrid attack" to retaliate against EU sanctions on his government for its crackdown on domestic protests after his disputed 2020 re-election.
Russian-backed Belarus denies the allegations but says it will no longer stop refugees and migrants from trying to enter the EU.
The Belarusian Defence Ministry accused Poland on Thursday of an "unprecedented" military build-up on the border, saying migration control did not warrant the concentration of 15,000 troops backed by tanks, air defence assets and other weapons.
Watch: Russia sends nuclear-capable bombers over Belarus in show of support on Wednesday.
Russia has sent paratroopers to Belarus in a show of support for its ally amid the tensions.
The Russian Defence Ministry said that as part of joint war games, Russian troops will parachute from Il-76 transport planes in Belarus' Grodno region, which borders Poland.
The Belarusian military said the exercise involving a battalion of Russian paratroopers was intended to test the readiness of the allies' rapid response forces due to an "increase of military activities near the Belarusian border".
It added that, as part of drills which will also involve Belarusian air defence assets, helicopter gunships and other forces, troops will practise targeting enemy scouts and illegal armed formations, along with other tasks.
In a statement, NATO said: "The North Atlantic Council strongly condemns the continued instrumentalisation of irregular migration artificially created by Belarus as part of hybrid actions targeted against Poland, Lithuania, and Latvia for political purposes.
"These callous actions endanger the lives of vulnerable people. NATO Allies stand in solidarity with Poland, Lithuania, Latvia, and other Allied nations affected, and support measures, guided by fundamental values and applicable international law, taken by Allies individually and collectively, in response to a situation that requires close coordination with key international partners.
"We will remain vigilant against the risk of further escalation and provocation by Belarus at its borders with Poland, Lithuania, and Latvia, and will continue to monitor the implications for the security of the Alliance. NATO Allies call on Belarus to cease these actions, to respect human rights and fundamental freedoms, and to abide by international law."