A new prisoner swap between Ukraine and Russia has begun, officials in both countries said Monday, with Ukrainian soldiers who have spent nearly the entire duration of the war in captivity among those returning home.

Russia and Ukraine exchange prisoners of war who are under the age of 25, marking the first steps of a series of planned prisoner swaps.

CHERNIHIV, Ukraine — Russia and Ukraine carried out an exchange of prisoners of war on Monday involving POWs under the age of 25 and others who had been severely wounded, marking the start of what could become the biggest swap of the conflict so far.