Russia's Federal Security Service on Friday accused six British diplomats of spying and said a decision has been made to withdraw their accreditation.

Russian state TV quoted an official from the security service known as the FSB as saying that they will be expelled. The expulsions come as Prime Minister Keir Starmer visits Washington for talks with U.S. President Joe Biden that will include Ukraine's request to use Western-supplied weapons against targets inside Russia.

Starmer said on his way to the U.S. that Britain does not "seek any conflict with Russia."

"Russia started this conflict. Russia illegally invaded Ukraine. Russia could end this conflict straight away," he told reporters.

"Ukraine has the right to self-defence and we've obviously been absolutely fully supportive of Ukraine's right to self-defence — we're providing training capability, as you know. But we don't seek any conflict with Russia — that's not our intention in the slightest."

Russian President Vladimir Putin in turn warned that allowing long-range strikes "would mean that NATO countries, the United States and European countries are at war with Russia ... if this is so, then, bearing in mind the change in the very essence of this conflict, we will make appropriate decisions based on the threats that will be created for us."

Long-range U.S. Army Tactical Missile Systems (ATACMS) have a range of up to 305 kilometres, while the British Storm Shadows have a reach of around 250 km.

Ukraine is already firing both at Russian targets on territory internationally recognized as Ukraine, but wants to use them to hit bases inside Russia itself.

WATCH l U.S. not sure expanding missile parameters would be a game changer:

Ukraine pleads to use Western weapons further into Russia

Ukraine is again pleading for restrictions to be lifted on using long-range Western missiles to hit further into Russia, but some other countries aren’t sure it’s necessary because Ukraine is already using drones to strike targets far beyond the border.

'Completely baseless' allegations: Britain

The FSB said it received documents indicating that the diplomats were sent to Russia by a division of the U.K. Foreign Office "whose main task is to inflict a strategic defeat on our country," and that they were involved in "intelligence-gathering and subversive activities."

Based on these documents and "in response to numerous unfriendly steps by London," the Russian Foreign Ministry withdrew the accreditation of the diplomats, the FSB said, without identifying them. It warned that if other diplomats are found to be carrying out "similar actions," the agency "will demand early termination of their missions" to Russia.

Russian state TV said in a report that the six diplomats had met with independent media and rights groups that have been declared "foreign agents" — a label the Russian authorities have actively used against organizations and individuals critical of the Kremlin.

Russian Foreign Ministry spokesperson Maria Zakharova said in an online statement that: "We fully agree with the assessments of the activities of the British so-called diplomats expressed by the Russian FSB. The British Embassy has gone far beyond the limits outlined by the Vienna Conventions."

She said the diplomats were carrying out "subversive actions aimed at causing harm to our people."

Britain called the allegations against the diplomats "completely baseless."

It said the expulsions happened weeks ago, linking them to Britain's decision in May to revoke the credentials of an attaché at Moscow's London Embassy and to impose a five-year time limit on all Russian diplomats in Britain. About a week later, Russia reciprocated and expelled Britain's defence attaché.

Expulsions more common

Expulsions of diplomats — both Western diplomats working in Russia and Russian diplomats working in Western countries — have become increasingly common since Russia invaded Ukraine in February 2022. 

Russian news outlet RBC counted last year that Western countries and Japan expelled a total 670 Russian diplomats between the beginning of 2022 and October 2023, while Moscow expelled 346 diplomats in response. According to RBC, it was more than in the previous 20 years combined.

Britain has also expelled Russian diplomats after high-profile attacks on U.K. soil, as when former FSB agent Alexander Litvinenko was fatally poisoned in 2006, and in a co-ordinated action with Western allies such as the U.S. and Canada after former Russian spy Sergei Skripal and his daughter were hospitalized for weeks after a 2018 nerve-agent poisoning in Salisbury, England.

Russia denied involvement in the Litvinenko and Skripal attacks.