LONDON — On Monday, among the embassies dotting London’s Belgrave Square, a Ukrainian flag hung from a window of one of the white stucco mansions. Another banner hanging from the balcony below read, “This property has been liberated.”
A group of people in balaclavas sat on the balcony, dangling their feet, waving at a small group of supporters as the police surrounded the area.
On Sunday night, the group broke into the house to protest against President Vladimir V. Putin’s invasion of Ukraine. The home is one of the addresses of the Russian oligarch Oleg Deripaska, who is on the sanctions list of the U.S. Treasury Department.
“You occupy Ukraine, we occupy you,” a flyer for the initiative from the self-described anarchists read, adding that the mansion, which belonged to a “Russian oligarch, complicit of Putin’s invasion,” would host Ukrainian refugees.
Britain has recently committed to tightening laws on oligarchs. On Friday, it added Mr. Deripaska, who is a well-connected industrialist and was known for being close to Mr. Putin, to a sanctions list, along with six other oligarchs.
The British government also said Sunday that it would explore the possibility of using the homes of sanctioned individuals for humanitarian purposes.
Mr. Deripaska has been one of the few oligarchs speaking out against the war in Ukraine, calling for peace and calling the war “madness.” He has also opposed the sanctions, saying on Twitter that there was not a “single fact” supporting the cabinet’s decision to add him to the list.
According to court documents from 2006, Mr. Deripaska was the beneficial owner of the occupied house but Mr. Deripaska’s spokeswoman said that the house belongs to members of his family and not to him personally.
“We are appalled at the negligence of Britain’s justice system shown by Boris Johnson’s cabinet in introducing the sanctions and colluding with the sort of people who raid private property,” the spokeswoman, Larisa Belyaeva, said in an email.
She added that the “Russia witch hunt” will eventually end but that “it’s truly a disgrace that this is happening in a country that is supposed to respect private property and the rule of law.”
Pictures of the mansion from a 1938 issue of Country Life magazine show lavish rococo interiors. In 2002, when the house was on the market, it was reportedly one of the last private houses in a square mostly used by embassies and institutions. It had seven reception rooms, seven bedrooms and a Turkish steam bath.
The protesters told reporters they got lost many times in the house.
Jochen Lukesch, 61, a retired schoolteacher, jumped out of his bed in a suburb in east London when he heard on the radio that the mansion had been occupied. He wrapped himself in a Ukrainian flag and rushed to Belgrave Square.
“So this is where the gangsters live,” he said, as he marveled at the mansions before joining a small crowd of supporters and shouting “Slava Ukraini,” or glory to Ukraine.
London’s Metropolitan Police said officers were called to the property early Monday and found only a few protesters on the balcony. On Monday afternoon, they detained two people who attempted to breach the police cordon around the building.
Tatiana Golovina, 59, a Russian entrepreneur who had to take a detour to make it to her home near Belgrave Square because of the protest, disagreed. She decried the war in Ukraine but said occupying private property wasn’t the answer.
“It’s barbaric,” she said, as she took a picture of the occupation, “it reminds me of the Russian Revolution in 1917.”