Russia and Ukraine began a major prisoner swap on Friday expected to be the biggest of the war, as agreed to last week at their first direct talks in more than three years, a Ukrainian military source said.

Ukrainian authorities told reporters to assemble at a location in the northern Chernihiv region in anticipation that some freed prisoners could be brought there. The Ukrainian military source said the swap was still underway.

By mid-afternoon Moscow time, Russian state media had not yet reported the exchange was underway, and the Russian defense ministry did not immediately respond to a request for comment.