Russia's Defense Ministry said Ukraine had handed over 50 captured Russian service personnel on Thursday in the latest prisoner exchange between the two sides.
Earlier on Thursday, the top Russian-installed official in Ukraine's partly-occupied Donetsk region said Moscow and Kyiv would each hand over 50 prisoners of war.
Russia said it would fly the released prisoners to Moscow for medical checks and rehabilitation.
Ukraine says Russia 'distracting' air defenses with dud nuclear-capable missiles
Ukraine's military said on Thursday it had found fragments of Russian-fired nuclear-capable missiles with dud warheads in west Ukraine, and that their apparent purpose was to distract air defenses.
Mykola Danyliuk, a representative of the Ukrainian armed forces' research unit, told a briefing that missile fragments that fell in the western regions of Lviv and Khmelnytskyi on Oct. 31 had been identified as parts of Kh-55 cruise missiles.
The Kh-55 was designed by the Soviet Union in the 1970s for use on strategic targets. It is primarily intended to carry nuclear warheads and to be launched from bomber aircraft.
The official said a test on the fragments did not show abnormal levels of radioactivity.
"This shows that there was no contact (of the missile) with nuclear elements," he said.
Russia's Defense Ministry did not immediately respond to a request for comment.
Danyliuk said the missiles were fitted with non-explosive warheads, one of which was exhibited on the stage of the briefing center in Kyiv where he was speaking.
"This is a substitute for a thermo-nuclear guided charge," he said.
Danyliuk said the Kh-55 had not been used by Russia in Ukraine before Oct. 31.
"The uniqueness of the missiles discovered was that they were equipped with a non-explosive warhead," Danyliuk said.
Even so, the missile presented a degree of danger because of its kinetic energy and fuel, he said.
"This is evidenced by... the impact of a Kh-55 missile into a residential building," he said.
"We can state that the launch of these missiles is intended to... distract the attention of Ukraine's air defense system and tire it out, while modern Russian rockets... are fired on critical infrastructure objects."
Danyliuk also said that all the Kh-55 missiles that had been discovered had their serial numbers scratched out.