"I have just signed a letter to the president of the UN Security Council asking him to convene a meeting of the Security Council as soon as possible in connection with the escalation of Russia's missile terror against civilians in Ukraine," Ukraine's UN ambassador Andriy Melnyk told Ukrinform.
Ukrainian officials declared a day of mourning on Wednesday for victims of what President Volodymyr Zelenskiy described as one of the most horrific attacks on the capital during the war in which a section of a Kyiv apartment block was flattened.
It comes as Zelenskiy arrived in Canada on Tuesday to urge the G7 to provide more backing for the war against Russia even after US President Donald Trump left the summit early due to developments in the Middle East.
Zelenskiy started his day by meeting Canadian Prime Minister Mark Carney, who said his country would provide $C2 billion ($A2.25 billion) in new military assistance for Ukraine.
The Russian attack overnight on Kyiv that killed 12 people "underscores the importance of standing in total solidarity with Ukraine," he said.
The United States condemned the attack on Kyiv, State Department spokeswoman Tammy Bruce said on Tuesday, confirming the death of a US citizen in Ukraine.
"We are aware of last night's attack on Kyiv, which resulted in numerous casualties, including the tragic death of a US citizen. We condemn those strikes and extend our deepest condolences to the victims and to the families of all those affected," Bruce told reporters.
Carney said when G7 leaders met for dinner on Monday, they stressed the importance of using "maximum pressure against Russia" to force it to start serious peace talks.
"We are ready for the peace negotiations, unconditional ceasefire - I think it's very important. But for this, we need pressure," Zelenskiy replied.
When the summit ends later on Tuesday, Carney plans to issue a statement calling for more pressure on Russia through sanctions and saying the G7 backs US-led peace efforts, a G7 source said.
Although Canada is one of Ukraine's most vocal defenders, its ability to help Ukraine's military is far outweighed by the United States, the largest arms supplier.
Zelenskiy had said he hoped to talk to Trump about acquiring more weapons.
A European Union diplomat said all remaining G7 members wanted to stay to meet Zelenskiy and continue conversations.
