By Dominic Giannini in Canberra

Australia should use frozen Russian assets to rebuild a critical hospital hit in a barrage of missiles, Ukraine’s ambassador says as the federal government condemns the attack.

Vasyl Myroshnychenko branded the incident as horrible and “one of the worst attacks ever”.

A day of mourning has been declared after at least 36 civilians were killed in the deadliest wave of strikes against Ukraine in months.

“That was a very important children’s hospital, it was specifically dealing with some very complicated cases,” the ambassador told AAP.

“The brand new building which was recently completed which included the cancer ward and toxicology ward … when you can think Russia cannot go lower, they are always finding a way.”

Prime Minister Anthony Albanese condemned the attack, describing it as abhorrent.

“It is time, well past time for Vladimir Putin to end this conflict,” he told reporters in Sydney.

“Russia’s actions continue to shock the world. At the NATO summit … no doubt this will be a topic as well.”

Mr Myroshnychenko told reporters in Canberra he would also welcome Australia joining a security guarantee signed with G7 nations and hoped for a new military aid package when NATO members meet in Washington.

Defence Minister Richard Marles is representing Australia at the summit and will meet with Ukrainian President Volodymyr Zelenskiy.

“The best way you can respond to this is of course to provide more military assistance to Ukraine,” Mr Myroshnychenko said while praising Australia’s previous contributions.

“Ukraine needs some modern air defence systems and we need to have the tools and equipment to be able to push Russians out.

“But this is of course up to the Australian government.”

Defeating Russia was also important to the Indo-Pacific region with the Kremlin recently signing a security pact with North Korea, he added.

Foreign Minister Penny Wong joined the international community in expressing outrage at the missile strike on the children’s hospital.

“Russia’s missile attacks on several Ukrainian cities, including a Kyiv children’s hospital are abhorrent,” she wrote on social media site X.

“Australia continues to support the people of Ukraine in the face of Russia’s illegal, immoral war.”

Two children were among 22 people killed in the capital with more than 80 others wounded, according to Ukrainian officials.

Scores more were killed and injured in other regions during the barrage of missiles.

Watching the footage of children being treated out in the open was “gut-wrenching”, Mr Myroshnychenko said.

“We are still counting the number of casualties but it has definitely been one of the most terrible attacks,” he said.

Kyiv has called the attack a war crime.

Mr Zelenskiy has vowed to retaliate as Kyiv sought more air defence systems to help protect cities and civilians.

“The question to our partners is: can they respond?” he said, with the attack coming as NATO countries are set to meet in Washington.

Russia claims it carried out strikes against defence industry targets and has previously denied targeting civilians.

–with Reuters