HORLIVKA, Ukraine (AP) — Ukrainian authorities and Russian-backed separatist rebels conducted a massive prisoner exchange Wednesday, the largest such trade of captives since the start of an armed conflict in the country's east and a sign of visible progress in the implementation of a 2015 peace deal.

Rebels from the self-proclaimed separatist republics in the Luhansk and Donetsk regions handed over 74 prisoners, and Ukrainian authorities delivered 233. Some had been held for more than a year.

Larisa Sargan, a spokeswoman for the country's prosecutor general's office, said on Facebook that one...