Britain's Prime Minister Rishi Sunak plans to announce a ban on Russian diamonds and imports of metals from Russia including copper, aluminium and nickel in support for Ukraine, his government said in a statement.

Britain is also targeting an additional 86 people and companies from Russian President Vladimir Putin's military industrial complex, in addition those involved in energy, metals and shipping industries.

They include those supporting the Kremlin to actively undermine the impact of existing sanctions, as Britain continues to work with G7 partners to tackle all forms of sanctions circumvention, the government said.

On Monday, Britain promised Ukrainian President Volodymyr Zelenskiy long-range attack drones when he visited the country as part of a European tour aimed at securing new weapons for a counteroffensive against Russia.

Leaders of advanced democracies Japan, the United States, Germany, Britain, France, Canada and Italy start their Group of Seven (G7) summit on Friday in Hiroshima.

The G7 countries are poised to use the summit to announce tightened sanctions on Russia and debate strategy on a more than year-long conflict that shows no sign of easing.