The EU has imposed sanctions on the Kremlin-linked Wagner Group for sending mercenaries to conflict zones and violating international humanitarian law.
Foreign ministers from the bloc levied asset freezes, travel bans and financial restrictions on the private military company itself, eight individuals and three entities connected to it.
The EU said the individuals were involved in serious human rights abuses and destabilising activities in Libya, Syria, Ukraine's Donbass region and the Central Africa Republic.
“The group is also spreading its malign influence elsewhere, notably in the sub-Sahara region,” the EU said.
It added that those sanctioned were involved in torture and executions, and destabilising activities in the countries they operated in.
The move came as European foreign ministers discussed another potential round of sanctions against Russia and worked to avoid a crisis amid a build of Moscow’s troops on its border with Ukraine.
EU foreign affairs chief Josep Borrell, speaking after the meeting in Brussels, said ministers were in agreement that Russian aggression against Ukraine would come with "political consequences" and “high economic cost" Moscow.
Mr Borrell said ministers were in a “deterring” and “dissuasion mode” to prevent a crisis developing and military action happening. "Once it starts, it's very difficult to stop," he added.
Speaking on arrival to the talks, he said no “concrete decision” would be taken on sanctions on Monday. The EU is studying, in coordination with the US and UK, what and when those next economic measures could be, he added.
“But in any case we will send a clear signal that any aggression against Ukraine will have a high cost for Russia, if it happens. But, now, we are trying to do our best in order to prevent this from happening,” Mr Borrell said.
His comments echo those of G7 countries at the weekend, when they warned Russia of consequences if it takes action against Ukraine.
EU measures were imposed in 2014 on Russia’s energy, banking and defence sectors, after it invaded Ukraine and annexed Crimea.
Russia has massed 90,000 troops at its border with Ukraine and has backed separatists fighting Ukrainian government forces. Efforts to reach a political settlement to a separatist conflict that has killed more than 14,000 people in seven years have so far failed.
While western leaders say they fear an attack, Russia insists it has no such intention.
Lithuanian Foreign Minister Gabrielius Landsbergis, whose country has an uneasy relationship with its Russian neighbour, said: “We are convinced that Russia is actually preparing for all-out war against Ukraine. It's an unprecedented event probably since the Second World War.
“If it's an unprecedented attack … that means that the answer has to be unprecedented from Western countries as well.”
Mr Borrell said Monday’s talks were in a way a continuation of the weekend’s G7 talks, where he said there was a strong agreement to “stand behind Ukraine” and “its sovereignty and territorial integrity”.