Kyiv (Ukraine) (AFP) - The United States and other G7 powers will hold crisis talks Tuesday on Russia's recent bombing blitz across Ukraine, with Britain's Liz Truss expected to insist they "must not waver one iota" in their support for Kyiv.

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".

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.

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.

'Stay the course'

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

Truss's office said the British prime minister, who succeeded Boris Johnson just over a month ago, would use the call "to urge fellow leaders to stay the course".

"The overwhelming international support for Ukraine's struggle stands in stark opposition to the isolation of Russia on the international stage," she is expected to say.

"Nobody wants peace more than Ukraine. And for our part, we must not waver one iota in our resolve to help them win it."

German government spokesman Steffen Hebestreit told reporters Monday that Chancellor Olaf Scholz had spoken with Zelensky and assured him "of the solidarity of Germany and the other G7 states".

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

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".

'In an instant... it's death'

Residents across Ukraine expressed shock and rage after Monday's barrage.

Ivan Poliakov, 22, was so angry he struggled for words as he tried to describe one of the strikes on Kyiv.

"I saw children and women cry," he told AFP. "I love Kyiv. The people are good, they are courageous. But in an instant... it's death."

In Dnipro, soldier Maxim was on leave from the front lines for the first time in six months to celebrate his wife's birthday when Russian missiles slammed into the central Ukrainian city, damaging their home.

"We are fighting on the front exactly to protect these places" far from enemy lines, he said. "But they still manage to hit them."

The strike, he said, had made him more determined than ever to push back the Russians in northeast Ukraine.

Since Russia launched its invasion on February 24, more than 7.6 million Ukrainian refugees have been recorded across Europe, while another nearly seven million people have been displaced within the country.

Monday's missile strikes prompted a fresh warning from the UN's refugee chief that more people could soon be forced to flee their homes.

"The bombing of civilians, of houses... of non-military infrastructure in an indiscriminate manner in many cities across Ukraine, means the war is becoming harder and more difficult for civilians," UN High Commissioner for Refugees Filippo Grandi told journalists in Geneva.

"I fear that the events of these last hours will provoke more displacements."