US President Joe Biden accused Russia of committing "major war crimes" in Ukraine on Wednesday and vowed to inflict more costs on Moscow.

Speaking in an address to trade leaders, Biden invoked gruesome photos of slain people in the Ukrainian city of Bucha, which he said showed "civilians (were) executed in cold blood, bodies dumped into mass graves."

"There's nothing less happening than major war crimes. Responsible nations have to come together to hold these perpetrators accountable," said Biden.

"Together with our allies and our partners, we're going to keep raising economic costs, and ratchet up the pain for (Russian President Vladimir) Putin and further increase Russia's economic isolation," he said.

The images of apparent brutal killings of civilians emerged from Bucha earlier this week, which was formerly occupied by Russian forces. Russia withdrew from the area on March 30.

Putin and Moscow are facing vehement criticism from the international community after Ukraine accused Russian forces of committing “genocide” and “war crimes” in Bucha.

Russia has rejected the allegations as a “fake news attack,” arguing that the images that have drawn global outrage were staged after Russian forces withdrew from the city.

The Russia-Ukraine war has drawn international outrage, with the EU, US, and Britain, among others, implementing tough financial sanctions on Moscow.

At least 1,563 civilians have been killed in Ukraine and 2,213 injured, according to UN estimates, with the true figure feared to be far higher.

More than 4.27 million Ukrainians have fled to other countries, with millions more internally displaced, according to the UN refugee agency./aa