Russia has committed wide-ranging war crimes in Ukraine such as wilful killings, torture and the deportation of children, a UN-mandated investigative body said in a report published on Thursday.

The report, based on more than 500 interviews as well as satellite images and visits to detention sites and graves, comes as the International Criminal Court in The Hague is expected to seek the arrest of Russian officials for forcibly deporting children from Ukraine and targeting civilian infrastructure.

The Independent International Commission of Inquiry on Ukraine said that Russian forces have carried out "indiscriminate and disproportionate" attacks on Ukraine, resorted to torture, killed civilians outside of combat and failed to take measures to safeguard the Ukrainian population.

"Russian authorities have committed numerous violations of international humanitarian law and violations of international human rights law, in addition to a wide range of war crimes...," the report said.

The document gave details of torture methods used in Russian detention facilities where victims were subjected to electric shocks with a military phone - a treatment known as a "call to (Russian President Vladimir) Putin" - or hung from the ceiling in a "parrot position".

Russia denies committing atrocities or targeting civilians in Ukraine.