The UK announced Thursday dozens of new sanctions aimed at constraining Russia's war in Ukraine, including targeting Moscow's main stock exchange, a day after Washington announced similar measures.

London said the 50 new curbs -- part of "coordinated action with G7 partners" as the Western-led bloc's leaders meet in Italy -- will hit the Russian financial system and suppliers supporting its military production.

It follows Washington on Wednesday unveiling a raft of sanctions, including on the Moscow exchange and several subsidiaries, which raise the stakes for foreign banks that still deal with Russia.

The major new financial punishment, set to complicate billions of dollars in transactions, prompted the exchange to halt dollar and euro trades on Thursday.

Moscow's foreign ministry has said it will respond to the "aggressive" raft of new US sanctions.

Prime Minister Rishi Sunak said the UK "will always stand shoulder to shoulder with Ukraine in its fight for freedom".

"Today we are once more ramping up economic pressure through sanctions to bear down on Russia's ability to fund its war machine," he added, as G7 leaders convene for their summit in southern Italy.

Russian President Vladimir Putin "must lose, and cutting off his ability to fund a prolonged conflict is absolutely vital", Sunak said.

Among the new UK sanctions are its first sanctions on vessels in Putin's so-called shadow fleet, used by the Kremlin to circumvent Western curbs on its oil exports.

They also target suppliers of munitions, machine tools, microelectronics, and logistics to Russia's military, Sunak's Downing Street office said.

Those suppliers include entities based in China, Israel, Kyrgyzstan and Turkey, along with ships which transport military goods from North Korea to Russia.

British Foreign Secretary David Cameron told reporters in London the government's use of sanctions was no longer restricted to companies and individuals operating in the UK or Europe.

"We are chasing companies across the world... we're going after the money, we're going after the oil, we're stopping the gas, we're stopping the ships. We're doing everything we can to stop the Russian war machine," he said.

Sunak's office noted it was also "working with counterparts to agree a mechanism to bring forward the extraordinary profits stemming from immobilised Russian sovereign assets to the benefit of Ukraine".

The White House has said that steps to aid Ukraine using frozen Russian assets will be announced during the G7 gathering.