HIROSHIMA, JAPAN - The United States unveiled "significant" new sanctions targeting Russia's "war machine" on Friday, as President Joe Biden meets fellow G7 leaders in Japan.

The heads of seven wealthy democracies are gathered in Hiroshima, where they will discuss tightening the screws on Russia's ailing economy as well as how to respond to China's growing military and economic power.

Washington got the ball rolling Friday, with a senior US administration official promising "a significant effort that will extensively restrict Russia's access to goods that matter for its battlefield capabilities".

"It will cut off roughly 70 entities from Russia and other countries from receiving US exports by adding them to the Commerce blacklist. And there will be upwards of 300 new sanctions against individuals, entities, vessels and aircraft," the official said.

Other G7 members are also preparing to "implement new sanctions and export controls", he added.

The bloc wants to disrupt Russian war supplies, close evasion loopholes and further reduce reliance on Russian energy, he said.

It will also continue to squeeze Moscow's access to the international financial system and commit to keeping Russian assets frozen until the end of the war in Ukraine.

On Thursday, a European Union official said one potential target for discussion was Russia's multi-billion-dollar diamond industry.

"We believe we need to limit exports from Russian trade in this sector," the official said, adding that Indian buy-in would be crucial to making any new measures work.

China 'de-risking'

Apart from Ukraine, China will dominate the three days of meetings.

There the focus will be on diversifying crucial supply chains away from China and insulating sectors from "economic coercion".

But European countries insist that doesn't mean breaking ties with China, one of the world's largest markets.

"Not a single country" is pursuing "decoupling", German Chancellor Olaf Scholz told reporters in Hiroshima.

"However, we want to organise global supply relations, trade and investment relations, in such a way that the risks are not increased by dependence on individual countries," he said.