An advance team left the International Criminal Court (ICC) in The Hague for "the Ukraine region" on Thursday to start investigating possible war crimes, its top prosecutor told Reuters in an interview.

Their departure came hours after Prosecutor Karim Khan said he would start collecting evidence as part of a formal investigation launched after Russia's full-scale invasion of Ukraine that began on Feb. 24.

"Yesterday I formulated a team and today they are moving to the region," Khan said. "It's an advanced team, comprised of investigators, lawyers, but also those with particular experience in operational planning."

Khan said his office would be examining possible war crimes, crimes against humanity and genocide - the offences under the court's jurisdiction - by all parties in the conflict.

Neither Russia nor Ukraine are members of the ICC, and Moscow does not recognise the court, which was established in 1997 by the Rome Statute and opened in The Hague in 2002.

Though not a member of the ICC, Ukraine signed a declaration in 2014 giving the court jurisdiction over alleged grave crimes committed on its territory from 2014 onwards regardless of the nationality of the perpetrators.

'LAWS OF WAR'

The ICC, which has 123 member states, prosecutes individuals responsible for the worst atrocities when a country is unable or unwilling to do so.

"The law of war continues to apply and we have clear jurisdiction," Khan said. "This is a reminder to all factions, to all parties to the conflict, that they must conduct themselves in compliance with the laws of war."

Asked about attacks with cluster bombs and artillery strikes in Ukraine's towns and cities, Khan said: "Any side that targets, directly targets, civilians or civilian objects is committing a crime under the Rome Statute and under international humanitarian law. That much is clear."

The investigation will also look back to 2014, when Russia seized Ukraine's Crimea region and began providing support to armed separatists fighting Ukrainian government forces in the Donbass region in eastern Ukraine.

The prosecutor's 2020 annual report based on preliminary investigations cited suspected war crimes including killings and torture in Crimea and attacks on civilians, torture, murder and rape in eastern Ukraine.

If war crimes are found to have been committed in Ukraine, Khan said, his office would follow the evidence up the chain of command, to the highest levels of political and military office.

"Anybody involved in conflict needs to realise they don't have a licence to commit crimes," he said.