Defence Secretary John Healey said Nato would meet Moscow’s “escalation with our strength” ahead of a meeting of the defence alliance amid a surge in Russian drone strikes in Ukraine and “totally unacceptable” incursions into European airspace.
Meanwhile, the chairman of Ukraine’s parliament hailed the coming-into-force of a long-term UK-Ukraine partnership deal during a visit to Westminster on Wednesday.
Mr Healey will attend the first gathering of Nato defence ministers since a series of drones violated European skies in recent weeks.
The alliance is seeking to bolster defences on Europe’s eastern flank after its jets downed drones over Poland and Estonia said Russian jets flew into its territory.
He is also co-hosting the latest meeting of the Ukraine Defence Contact Group in Brussels.
The Cabinet minister said: “The UK and Nato nations are meeting today to ramp up our response to Russia’s aggression.
“(Vladimir) Putin’s incursions into Nato territory are reckless, dangerous and totally unacceptable.
“Deliberate or not, Putin is watching what we do. And Putin should be in no doubt: if Nato is threatened, we will act.
“And we must meet his escalation with our strength.”
Mr Healey confirmed the UK’s participation in Nato’s Eastern Sentry mission, with RAF Typhoon fighter jets patrolling Poland after Russian drone incursions last month, will continue until the end of the year.
He also announced an increase in drone production for Ukraine, with the UK delivering more than 85,000 of the weapons over the last six months.
The UK will also deploy military counter-drone experts to Moldova.
He added: “Putin seeks to test, to divide, to distract. Nato nations step up to deter, to unite, stronger together than ever.”
Mr Healey is expected to hold a press conference at 5.40pm alongside Ukraine’s defence minister Denys Shmyhal and Germany’s Boris Pistorius.
Elsewhere, Ruslan Stefanchuk, the chairman of Ukraine’s Verkhovna Rada, celebrated the 100 Year Partnership Agreement entering into force as he visited London.
The deal was signed by Sir Keir Starmer and Ukrainian President Volodymyr Zelensky in Kyiv in January with the aim of boosting defence and scientific collaboration and forging new community links between the two countries.
Mr Stefanchuk told a crowd of parliamentarians gathered in Portcullis House that he was delivering a diplomatic note bringing the deal into effect.
The Ukrainian politician also said democratic countries have “no right to turn a blind eye” to Moscow’s continued destruction of Ukrainian critical infrastructure, killing of civilians and abduction of children.
Russia must receive a firm response in the form of sanctions “that cannot be avoided or circumvented”, and frozen Russian assets must be used to compensate for the damage it has caused, he said.
“Russia not only sows death and continues its aggression — it keeps testing the limits of what is allowed,” Mr Stefanchuk said.
“Today, on the eve of a fourth winter of war — one that may prove to be among the most difficult in Ukraine’s modern history — we are in greater need than ever of the strengthening of your reliable assistance.”
He spoke next to a display of an Iranian-designed Shahed-136 drone that was shot down by the Ukrainian military.
Mr Stefanchuk is also set to attend Prime Minister’s Questions and hold meetings with the Prime Minister and the All-Party Parliamentary Group on Ukraine.
