Ukraine and Russia on Monday carried out the first stage of a prisoner exchange following agreements reached in Istanbul last week, Ukraine's Coordinating Headquarters for the Treatment of Prisoners of War reported.

The Russian Defense Ministry said in a statement that "the first group of Russian servicemen under the age of 25 was returned from the territory controlled by the Kiev regime."

A similar number of prisoners of war from the Ukrainian army were also transferred, it added.

During their last round of talks in Istanbul on June 2, Russia and Ukraine agreed on an "all-for-all" exchange involving seriously ill and wounded prisoners, as well as soldiers under the age of 25, according to Russian Presidential Aide Vladimir Medinsky.

Efforts remain ongoing to repatriate the bodies of Ukrainian servicemen, the Ukrainian agency said.