Lord Cameron said that British sanctions “deprive Putin of the resources he desperately needs to finance his faltering war.”
The UK announced more than 50 additional sanctions on Russia ahead of the second anniversary of the invasion of Ukraine.
The sanctions target individuals and companies that support Russian President Vladimir Putin's war effort.
Foreign Secretary Lord David Cameron said the UK would continue to support Kiev “as long as it takes”.
The Foreign Ministry said that the latest sanctions will take strict measures against those who supply the Russian military with munitions such as missile launch systems, missiles and explosives.
The sanctions also target Russia's main sources of revenue, clamping down on minerals, diamonds and energy trade, officials said, in a move aimed at cutting off funding for President Putin's war effort from every angle.
Announcing the new measures, Lord Cameron said: “Our international economic pressure means that Russia cannot afford this illegal invasion.
“Our sanctions deprive Putin of the resources he desperately needs to finance his faltering war.
He added: “Together, we will not relent in the face of tyranny. We will continue to support Ukraine in its struggle for democracy – for as long as it takes.”
Among those sanctioned are oil trader Niels Trost and his company Paramount Energy and Commodities SA, and Pavel Alekseevich Marinichev, the new CEO of Alrosa, Russia's largest state-owned diamond producer.
The State Department said several foreign companies were also targeted for their role in facilitating the Russian war effort.
Saturday marks the second anniversary of Russia's massive invasion of Ukraine.
The conflict has largely reached a stalemate, although Moscow appears to have made progress recently. Ukrainian President Volodymyr Zelensky has publicly urged Western allies to provide more weapons or risk emboldening Russian forces.
The European Union is working on its own package of measures to coincide with the war anniversary.
Alexei Navalny, pictured here at a rally in 2020, has been a vocal critic of President Vladimir Putin
The British sanctions come a day after the Foreign Office announced that it had frozen assets and imposed a travel ban on the heads of Russian prisons responsible for the penal colony where Alexei Navalny died.
These measures faced criticism from some quarters because they did not go further.
The government says it has imposed sanctions on 2,000 individuals, companies and groups under the Russian sanctions regime.
The United States has also pledged to impose new sanctions on Russia following Navalny's death, and they are expected to be imposed later this week.
Navalny, who was the most important Russian opposition leader over the past decade, was serving a 19-year prison sentence on charges that many considered politically motivated.
The Russian prison service said he died in the IK-3 Polar Penal Colony, nicknamed the “Polar Wolf”, on Friday last week after he was walking and then suddenly collapsed.
Navalny's team claims he was killed on the orders of President Putin. Western leaders also place the blame for his death squarely on Putin and Russian authorities.
Putin did not comment directly on his death. The Kremlin acknowledged his death and said that the Russian President was aware of it.
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