Ukraine needs to get younger people such as 18-25 year-old individuals into its war against Russia, US Secretary of State Antony Blinken said on Wednesday.

Having people on the battlefield, on top of ammunitions and weapons, was key to success, he said.

"These are very hard decisions," Blinken told Reuters in an interview in Brussels. "But, for example, getting younger people into the fight, we think, many of us think, is necessary. Right now, 18-25 year olds are not in the fight."