Russia unleashed a missile barrage across Ukraine on Wednesday, killing 10 people, forcing shutdowns of nuclear power plants and cutting water and electricity supply in many places.

Nevertheless, NATO's chief said that Russia, not Ukraine, was still to blame for starting the war in the first place with its February invasion and launching scores of missiles on Tuesday that triggered Ukrainian defences. 

Speaking by video link, Zelensky called the strike "a true statement brought by Russia for the G20 summit", according to a copy of his speech seen by AFP. 

Biden spoke after global leaders gathered for the G20 meeting in Bali, Indonesia, held an emergency meeting on Wednesday after deadly explosions in Poland that Ukraine and Polish authorities said were caused by Russian-made missiles.

Leaders from the United States, Germany, Canada, Netherlands, Japan, Spain, Italy, France and the United Kingdom were taking part in the meeting.

Warsaw put its military on heightened alert after an emergency national security council meeting.

The European Council president said an agreement regarding the Group of 20 statement had been reached at a preliminary meeting.

Briefing reporters ahead of President Joe Biden's participation in the summit, the official said most nations in the group had come together during talks in recent days and agreed that Russia's war in Ukraine should be "condemned in the strongest possible terms."

Ukrainian President Zelenskiy said he welcomed statements from the United States and China at meetings in Asia on the inadmissibility of threats to use nuclear weapons.

The Kremlin said that Putin would not even address the summit by video link.

Asked why Putin was not going to attend the G20 summit in Bali, Kremlin spokesman Dmitry Peskov said it was related to Putin's schedule and the need to stay in Russia.

"A number of specific initiatives are planned, including increasing gas cooperation with Turkey, (and) organising large shipments of grain and fertilisers," it said in a statement.

"I can confirm that (foreign minister) Sergei Lavrov will lead the Russian delegation to the G20. President Putin's program is still being worked out, he could participate virtually," said Yulia Tomskaya, the embassy's chief of protocol.

The 73-year-old monarch and Camilla, 75, appeared to be targeted with three eggs which landed near them during a walkabout in York, before they were ushered away by minders.

Russian President Vladimir Putin may opt to join the G20 Leaders' Summit virtually, President Joko "Jokowi" Widodo said on Tuesday, a week before the summit.

"The Russian Federation continues to commit its crimes in connection with Ukrainian children," Zelenskiy's office quoted Andriy Yermak as saying at a meeting he chaired of a group of officials responsible for child protection. "The removal of children continues."

Talks between the two sides on strategic stability have been frozen since Russia began its military campaign in Ukraine on Feb. 24, even as the New START treaty on nuclear arms reduction stays in effect.

Jokowi said a conversation with Putin last week left him with a "strong impression" the Russian leader would not attend the meeting in Bali, which is expected to be dominated by tensions over Russia's invasion of Ukraine.

"We need the United States and China to step up" on emissions cuts and financial aid, Macron told French and African climate campaigners on the sidelines of the UN climate summit in Sharm el-Sheikh, Egypt.

Scholz's comments came a day after his visit to the world's second-biggest economy alongside German corporate CEOs, the first by a G7 leader since the COVID-19 pandemic.

The newspaper cited unnamed sources as saying the request by American officials was not aimed at pushing Ukraine to the negotiating table, but a calculated attempt to ensure Kyiv maintains the support of other nations.

"If the leader of the Russian Federation was to take part in it, Ukraine would not be participating," Zelensky told a press conference with Greek President Katerina Sakellaropoulou in Kyiv. Putin is yet to say if he will attend.

"Had a phone conversation with President Putin and discussed about the Black Sea Grain Initiative. Welcome Russia’s decision to rejoin the initiative," President Joko "Jokowi" Widodo said in a tweet posted from his handle @jokowi on Wednesday evening.

"There is no long-term prosperity without action on climate change. There is no energy security without investing in renewables," Sunak wrote on Twitter.

Speaking in parliament, Erdogan said Russian Defence Minister Sergei Shoigu had informed his Turkish counterpart that the deal will resume.

"Putin publicly acknowledged ordering missile strikes on Ukrainian civilians and energy infrastructure," spokesperson Oleg Nikolenko wrote on Twitter.

US President Joe Biden denounced the move as "purely outrageous" and said it would increase starvation.

The two leaders held their first conversation after Sunak, a practising Hindu with Punjabi roots, became the UK's third leader in two months on Tuesday following the departure of Liz Truss. 

Charles is expected to amend the "Regency Act" to add his brother Edward, the Earl of Wessex, and his sister Anne, the Princess Royal, The Daily Telegraph and the BBC reported, quoting sources.

The leaders discussed the extent of UK-US cooperation, both bilaterally and in regions such as the Indo-Pacific where the AUKUS pact forms part of efforts to counter China's malign influence, the spokesperson said in a statement on Tuesday.