U.S. President Joe Biden and leaders of the Group of Seven (G7) countries were holding a virtual meeting on Wednesday with Ukraine's president, Volodymyr Zelenskiy, in a show of support for the country's war against Russia.

G7 countries were expected to announce a ban on Russian diamonds and measures to manage some 300 billion euros ($323.58 billion) in immobilised Russian central bank assets and the G7 oil price cap, sources familiar with the matter said.

Biden, meanwhile, was set to speak later on Wednesday pushing Congress to fund his weeks-old request for billions of dollars more in Ukraine assistance. The U.S. plans to announce $175 million in additional military aid for Ukraine on Wednesday, according to a U.S. official.

"We'd like to make clear that we stand with Ukraine as the G7," a Japanese government official said, adding the message would be reinforced amid concern that the international community's focus could shift away from Ukraine to the Middle East conflict.

The official, who declined to be named, said the G7 will reiterate its commitment to imposing strong sanctions on Russia for its attack on Ukraine, but details were being negotiated. The official did not elaborate.

Zelenskiy, addressing the meeting virtually, called for continued support for Ukraine.

"Russia believes that America and Europe will show weakness and will not maintain support for Ukraine at the proper level. Putin believes that the free world will not fully enforce its own sanctions," he said, according to remarks posted to the president's website.

"The free world vitally needs to maintain its consolidation, maintain interaction, maintain support for those whose freedom is being attacked."

The G7 members, comprising Japan, the United States, Canada, the United Kingdom, Germany, France, Italy and the European Union, pledged in May to restrict exports to Russia that could fund its war effort in Ukraine.

A statement issued at the time said the restrictions would cover exports of industrial machinery, tools and technology and it would also try to limit Russian revenues from trade in metals and diamonds.

Western nations have admitted that the impact of their $60 price cap on Russian crude oil has waned one year in, and the countries have been looking at ways to strengthen implementation.

Japan's chief cabinet secretary, Hirokazu Matsuno, said at a press conference on Wednesday that the G7 will also discuss the Middle East and artificial intelligence. A U.S. official said support for developing would also be a topic of conversation.

Russian President Vladimir Putin was in Saudi Arabia on Wednesday for talks with Crown Prince Mohammed bin Salman that were also expected to include Ukraine.