The UK has officially banned Russia's Wagner paramilitary group as a terrorist organisation, weeks after the death of its founder Yevgeny Prigozhin.
The order was approved on Friday – making it illegal to be a member of, or to support, Wagner.
Those found guilty of aiding the paramilitary could face steep fines and penalties of up to 14 years in prison.
Proposing the order last week, Home Secretary Suella Braverman called Wagner a "threat to global security".
"Wagner's continuing destabilising activities only continue to serve the Kremlin's political goals," Ms Braverman said.
"They are terrorists, plain and simple – and this proscription order makes that clear in UK law."
Under the order, it is a criminal offence to support the group. This includes arranging meetings to further its activities, expressing support for its aims and also displaying Wagner's flag or logo.
Those found guilty of supporting Wagner could be sentenced to up to 14 years in prison, or face a fine.
Wagner will now be added to a list of 78 other proscribed organisations in the UK, including as Hamas and Boko Haram.
The Wager paramilitary group, founded in around 2014 by Yevgeny Prigozhin, quickly became a key tool of Russian state power under President Vladimir Putin.
The group has helped to support allies of Mr Putin in countries such as Syria, Libya, Mali and the Central African Republic.
Its troops fought on the front lines following Russia's invasion of Ukraine, with the mercenaries heavily involved in the conflict in the east of the country. It was responsible for some of Russia's rare victories in cities such as Soledar and Bakhmut.
But Wagner's future was thrown into uncertainty earlier this year when Prigozhin led a failed mutiny against Russia's military leaders. He later died in a suspicious plane crash along with other Wagner figures on 23 August and was buried in St Petersburg.
On Friday, Kremlin spokesperson Dmitry Peskov denied that an investigation into the causes of the crash had been too slow, claiming that it was "not a simple investigation, not a simple incident".
"The investigation is ongoing, that is why giving some kind of commentary would be absolutely premature," he told reporters.
Senior MPs in the UK have been calling on the government to proscribe Wagner for months.
Earlier this year, Parliament's Foreign Affairs Select Committee produced a report condemning the government's "remarkably complacent" approach to the group and criticised its "dismal lack of understanding of Wagner's hold beyond Europe, in particular their grip on African states".
But the new ban could have come too late to have a real impact.
Last month, experts told the BBC that rival private military companies were seeking to take over Wagner, in the absence of Prigozhin's dominating leadership.
On Thursday, Alicia Kearns – chair of the Foreign Affairs Select Committee – urged the government to take "a more strategic approach towards [private military companies] operating across all conflict zones".
And the Labour's shadow foreign secretary David Lammy accused the government of being too slow to act and of "failing to keep up with changing threats to our national security".
This legislation has, in most people's view, come much too late.
As UK government lawyers were poring over the finer legal details, in preparation for the Home Office's announcement on 5 September of the intended ban, the Kremlin was already busy dismantling Wagner's power.
Never again could President Putin risk having such a well-armed paramilitary group challenge the authority of his generals.
The Wagner of today, though still potentially dangerous, is a shadow of what it was in the freewheeling days of its late leader, Yevgeny Prigozhin.
Most analysts now expect it to come more tightly under the control of the GRU, Russian military intelligence, and spend less time fighting and more on deniable, "grey zone" operations such as covert sabotage and cyber operations.
But as an extended arm of Kremlin policy in troubled parts of the world like Mali and Libya, Wagner – or whatever it may be rebranded as – still has the capacity to make money out of war, instability and alleged atrocities. To that end, banning it in Britain as a terrorist organisation has been largely welcomed.
Anton Mardasov, a non-resident scholar at the Middle East Institute's Syria Program, told the BBC that despite the loss of Prigozhin, Wagner had managed to "maintain some autonomy for now" in its more distant African deployments.
"Formally, it manages to survive and conduct business due to the fear of local authorities in the countries where Wagner is present for their regime and assets, so the threat of a gap and the activation of militants from the branches of Al-Qaeda and other radical groups helps Wagner," he said.
But in recent months Russia is said to have established dozens of new private military companies, all with varying loyalties to oligarchs, businesses and politicians.
And Arab media has reported that Russia's Deputy Defence Minister Yunus-bek Yevkurov ordered Wagner to either withdraw from Syria, or join Russian forces operating there by the end of September.
"The situation is explosive and there are no concrete prospects for its resolution yet," Mr Mardasov told the BBC.
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