Hiroshima, May 19: Leaders of the world's most powerful democracies vowed Friday to tighten punishments on Russia for its 15-month invasion of Ukraine, days before President Volodymyr Zelenskyy joins the Group of Seven summit in person on Sunday.

“Our support for Ukraine will not waver," the G7 leaders said in a statement released after closed-door meetings, vowing “to stand together against Russia's illegal, unjustifiable, and unprovoked war of aggression against Ukraine.” Russia-Ukraine War: Ukrainian President Volodymyr Zelenskyy Says Russian Troops Are Holding Zaporizhzhia Nuclear Plant 'Hostage'.

“Russia started this war and can end this war,” they said. Zelenskyy will be making his furthest trip from his war-torn country as leaders prepare to unveil new sanctions on Russia for its invasion. Oleksiy Danilov, the secretary of Ukraine's National Security and Defence Council, confirmed on national television that Zelenskyy would attend the summit. PM Narendra Modi Speaks to Ukraine President Volodymyr Zelenskyy, Discusses G20 Issues, Offers Support for Peace Efforts.

“We were sure that our president would be where Ukraine needed him, in any part of the world, to solve the issue of stability of our country,” Danilov said Friday. “There will be very important matters decided there, so physical presence is a crucial thing to defend our interests.”

Russian President Vladimir Putin's nuclear threats against Ukraine, along with North Korea's months-long barrage of missile tests and China's rapidly expanding nuclear arsenal, have resonated with Japan's push to make nuclear disarmament a major part of the summit.

World leaders Friday visited a peace park dedicated to the tens of thousands who died in the world's first wartime atomic bomb detonation. After group photos near the city's iconic bombed-out dome, a wreath-laying and a symbolic cherry tree planting, a new round of sanctions were to be unveiled against Moscow, with a focus on redoubling efforts to enforce existing sanctions meant to stifle Russia's war effort and hold accountable those behind it, a US official said.

Russia is now the most-sanctioned country in the world, but there are questions about the effectiveness of the financial penalties. The US official, speaking on the condition of anonymity to preview the announcement, said the US component of the actions would blacklist about 70 Russian and third-country entities involved in Russia's defence production, and sanction more than 300 individuals, entities, aircraft and vessels.

The official added that the other G7 nations would undertake similar steps to further isolate Russia and to undermine its ability to wage war in Ukraine. Details were to emerge over the course of the weekend summit.

The G7 nations said in Friday's statement that they would work to keep Russia from using the international financial system to prosecute its war, would “further restrict Russia's access to our economies” and would prevent sanctions evasion by Moscow. They urged other nations to stop providing Russia with support and weapons “or face severe costs.”

The European Union was focused on closing the door on loopholes and plans to restrict trade in Russian diamonds, Charles Michel, president of the European Council, told reporters early Friday.

Japanese Prime Minister Fumio Kishida, who represents Hiroshima in parliament, wants nuclear disarmament to be a major focus of discussions, and he formally started the summit at Hiroshima's Peace Memorial Park.

The visit by world leaders to a park dedicated to preserving reminders of August 6, 1945, when a US B-29 dropped an atomic bomb over Hiroshima, provided a striking backdrop to the start the summit.

An estimated 140,000 people were killed in the attack, and a fast-dwindling number of now-elderly survivors have ensured that Hiroshima has become synonymous with anti-nuclear peace efforts.

“Honestly, I have big doubts if Mr. Kishida, who is pursuing a military buildup and seeking to revise the pacifist constitution, can really discuss nuclear disarmament,” Sueichi Kido, a 83-year-old “hibakusha” or survivor of the Nagasaki explosion, told The Associated Press. “But because they are meeting in Hiroshima I do have a sliver of hope that they will have positive talks and make a tiny step toward nuclear disarmament.”

On Thursday night, Kishida opened the global diplomacy by sitting down with President Joe Biden after Biden's arrival at a nearby military base. Kishida also held talks with British Prime Minister Rishi Sunak before the three-day gathering of leaders opens.

The Japan-US alliance is the “very foundation of peace and security in the Indo-Pacific region,” Kishida told Biden in opening remarks. Japan, facing threats from authoritarian China, Russia and North Korea, has been expanding its military but also relies on 50,000 US troops stationed in Japan and US military might.

“We very much welcome that the cooperation has evolved in leaps and bounds,” Kishida said. Biden, who greeted US and Japanese troops at nearby Marine Corps Air Station Iwakuni before meeting with Kishida, said: “When our countries stand together, we stand stronger, and I believe the whole world is safer when we do."

As G7 attendees made their way to Hiroshima, Moscow unleashed yet another aerial attack on the Ukrainian capital. Loud explosions thundered through Kyiv during the early hours, marking the ninth time this month that Russian air raids have targeted the city after weeks of relative quiet.

The United States has frozen Russian Central Bank funds, restricted banks' access to SWIFT -- the dominant system for global financial transactions -- and sanctioned thousands of Russian firms, government officials, oligarchs and their families.

The Group of Seven nations collectively imposed a USD 60 per-barrel price cap on Russian oil and diesel last year, which the US Treasury Department on Thursday defended in a new progress report, stating that the cap has been successful in suppressing Russian oil revenues. Treasury cites Russian Ministry of Finance data showing that the Kremlin's oil revenues from January to March this year were more than 40 per cent lower than last year.

The economic impact of sanctions depends largely on the extent to which a targeted country is able to circumvent them, according to a recent Congressional Research Service report. So for the past month, US Treasury officials have travelled across Europe and Central Asia to press countries that still do business with the Kremlin to cut their financial ties.

“The challenge is to make sure the sanctions are painful against Russia, not against ourselves,” said Michel. “It's very clear that each package is more difficult than the previous one and requires more political effort to make a decision.”

G7 leaders and invited guests from several other counties are also expected to discuss how to deal with China's growing assertiveness and military buildup as concerns rise that it could could try to seize Taiwan by force, sparking a wider conflict. China claims the self-governing island as its own and its ships and warplanes regularly patrol near it.

In a bit of duelling diplomacy, Chinese President Xi Jinping is hosting the leaders of the Central Asian countries of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan for a two-day summit in the Chinese city of Xi'an.

The leaders are due to discuss efforts to strengthen the global economy and address rising prices that are squeezing families and government budgets around the world, particularly in developing countries in Africa, Asia and Latin America.

The debate over raising the debt limit in the US, the world's largest economy, has threatened to overshadow the G7 talks. Biden planned to hurry back to Washington after the summit for debt negotiations, scrapping planned meetings in Papua New Guinea and Australia.

The G7 includes Japan, the United States, the United Kingdom, France, Germany, Canada and Italy, as well as the European Union.