Home secretary Theresa May has said the Treasury will freeze the assets of the two prime suspects in the murder of Alexander Litvinenko, following the publication of a report decisively naming Andrei Lugovoy and Dmitry Kovtun.
The report, which said President Putin was "probably" involved in the operation, was "unequivocal," May said in the Commons this morning.
Although the government was still considering its response, she said the assets would be frozen, alongside Interpol notices and European arrest warrants being in place so that if Lugovoy and Kovtun travel, they can be arrested and extradited to the UK.
An extradition order has been in place for nearly 10 years but Russia has so far consistently refused to acknowledge it, May said.
Although there has been no formal statement on what, if any, wider measures may be brought, May was harsh in her condemnation of the state-sanctioned murder.
"The conclusion that Russian state was probably involved in the murder of Mr Litvinenko is deeply disturbing," May added. "It goes without saying that this was a blatant and unacceptable breach of the most fundamental tenets of international law and civilised behaviour."
She also paid tribute to Litvinenko's widow Marina.
Separately, the Russian ambassador Alexander Vladimirovich Yakovenko was summoned to the Foreign Office this afternoon to meet the minister responsible for Russia, David Lidington.
A Foreign Office spokeswoman said the Russian state's "probable involvement" in the murder was "deeply disturbing, demonstrating a flagrant disregard for UK law, international law and standards of conduct, and the safety of UK citizens".
"The minister said that this would further complicate bilateral relations, undermine trust, and damage Russia’s reputation internationally."
But others - notably Liberal Democrat leader Tim Farron - have gone further, echoing Marina Litvinenko's demands for heavier measures to be taken.
“I call for EU travel bans, asset freezes and coordinated action to deal with those who committed this evil assassination," Farron said. "I have called for a new Magnitsky Law to make sure that these people are held to account for what they did.
“These assassins trampled over British sovereignty and we cannot let this go unanswered.”