UK Prime Minister Liz Truss speaks during an interview. File photo

The meeting comes a day after Russian missiles rocked the Ukrainian capital for the first time in months, with President Volodymyr Zelensky warning Moscow that his country "cannot be intimidated".

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Russia unleashes biggest attacks in Ukraine

Explosions rock Ukrainian capital

Russian forces rained more than 80 missiles on cities across Ukraine on Monday, according to Kyiv, in apparent retaliation for an explosion that damaged a key bridge linking the Crimean peninsula to Russia.

Ukrainian Foreign Minister Dmytro Kuleba said the strikes showed Moscow was "desperate" after a spate of embarrassing military setbacks, as Russian President Vladimir Putin warned of "severe" responses to any further attacks.

Cars are on fire after Russia's missile attack in Kyiv, Ukraine, on Monday. Reuters

At an urgent meeting of the United Nations General Assembly on Monday — called to debate Moscow's declared annexation of four partly occupied Ukrainian regions — Ukrainian ambassador Sergiy Kyslytsya branded Russia a "terrorist state", noting his own immediate family had come under attack on Monday.

"Unfortunately, you can hardly call for a stable and sane peace as long as an unstable and insane dictatorship exists in your vicinity," he said, telling member states at least 14 civilians were killed and 97 wounded in the strikes.

Zelensky and G7 leaders are set to convene Tuesday to discuss the latest Russian attacks.

US President Joe Biden condemned Monday's attacks in stark terms, saying they "demonstrate the utter brutality" of Putin's "illegal war".

US President Joe Biden speaks during an event. File photo

In a statement, the White House said Biden had spoken to Zelensky and had pledged to furnish Ukraine with "advanced air defence systems".

Ahead of Monday's General Assembly session, UN Secretary-General Antonio Guterres described the latest attacks as an "unacceptable escalation of the war", his spokesman said.

Though Russian representative Vasily Nebenzya did not directly address the missile strikes at the session, he defended his country's annexation of Ukrainian regions, saying the aim was "to protect our brothers and sisters in eastern Ukraine".