Britain has sanctioned 12 members of Russian President Vladimir Putin's "inner circle" including his alleged girlfriend, accusing them of hiding tens of billions of dollars on his behalf.
The list included Mr Putin's ex-wife Lyudmila Ocheretnaya and Alina Kabaeva, a former Olympic gymnast whom UK officials described as his "current partner".
It also names Ms Kabaeva's grandmother Anna Zatseplina.
The European Union has proposed sanctioning Ms Kabaeva, according to a document seen last week by AFP. She is said by Western governments to be the mother of at least three of his children.
But the US government has held off targeting her, for fear of worsening hostilities with Vladimir Putin, according to a report last month by the Wall Street Journal.
"We are exposing and targeting the shady network propping up Putin's luxury lifestyle and tightening the vice on his inner circle," British Foreign Secretary Liz Truss said in a statement.
"We will keep going with sanctions on all those aiding and abetting Putin's aggression until Ukraine prevails."
The Kremlin leader's modest state salary and officially declared assets are belied by reports linking him to a luxury yacht and a sprawling property dubbed 'Putin's Palace', the UK statement said.
His true wealth is hidden by a network of family, childhood friends and members of the Russian elite who have been appointed to powerful roles "in return for their undying loyalty".
"These are people who deliberately lurk in the shadows to help Putin hide away his wealth," a UK official told reporters, on condition of anonymity.
Ms Kabaeva chairs Russia's National Media Group. The previously sanctioned Bank Rossiya owns one-third of the group and is a "clear channel" for President Putin's money, the official said.
Igor Putin, the Russian leader's first cousin, and Roman Putin, a first cousin once removed, were also among those targeted in the UK sanctions.
So was Alexander Plekhov, a "close friend" who controls the Vital Development Corp.
"We've identified tens of billions in assets" linked to Putin's inner circle, the UK official said.
Britain said it had now sanctioned more than 1,000 Russian individuals and 100 entities, including oligarchs worth more than €134 billion, since Mr Putin ordered the invasion of Ukraine in late February.
The UK has now targeted "almost all of the individuals and the entities that have been assessed as being closest to him, but of course we will keep going", the official said.
"The hit-list has certainly not finished yet."