"Well over" 100,000 Russian soldiers have been killed or wounded in the war in Ukraine, according to the US's top army general.

"Same thing probably on the Ukrainian side," said Mark Milley, chairman of the Joint Chiefs of Staff, on Wednesday. "There has been a tremendous amount of suffering, human suffering."

An estimated 40,000 Ukrainian civilians have been killed or wounded and anywhere between 15 million and 30 million Ukrainians have been displaced, he added.

The UN refugee chief recently put the figure at 14 million.

Russia has probably committed crimes against humanity by forcibly transferring Ukrainian civilians in Russian-occupied areas of the country to other regions, Amnesty International said on Thursday.

It said civilians were moved from occupied Ukraine further into Russian-controlled areas or into Russia, with children separated from their families in violation of international humanitarian law.

Amnesty said it had been told by civilians they had endured "abusive screening processes" - known as filtration - which sometimes resulted in arbitrary detention, torture and other ill-treatment.

"Separating children from their families and forcing people hundreds of kilometres from their homes are further proof of the severe suffering Russia's invasion has inflicted on Ukraine's civilians," said Agnes Callamard, Amnesty International's secretary general.

"Russia's deplorable tactic of forcible transfer and deportation is a war crime. Amnesty International believes this must be investigated as a crime against humanity," she said.

03:14 AM100,000 Russian troops killed or injured in Ukraine, US says 

"Well over" 100,000 Russian soldiers have been killed or wounded in the war in Ukraine, according to US Army General Mark Miley, chairman of the Joint Chiefs of Staff.

"Same thing probably on the Ukrainian side," Miley said on Wednesday. "There has been a tremendous amount of suffering, human suffering."

An estimated 40,000 Ukrainian civilians have been killed or wounded, he added.