Russia and Ukraine on Monday swapped a first group of captured soldiers — part of an agreement reached during peace talks that appeared to be in doubt over the weekend.

The deal to exchange prisoners of war and repatriate the bodies of killed fighters was the only concrete agreement reached at the talks, which have failed to lead to a breakthrough towards ending the three-year war.

Progress has stalled. Russia has issued tough conditions for halting its invasion and has repeatedly rejected calls for an unconditional ceasefire.

“Today an exchange began, which will continue in several stages over the coming days,” Ukrainian President Volodymyr Zelensky said on social media.

He posted images of soldiers draped in Ukrainian flags, cheering and hugging.

“Among those we are bringing back now are the wounded, the severely wounded, and those under the age of 25,” he added.

Russia’s defence ministry also confirmed the swap was part of “agreements reached on 2 June in Istanbul”.

Neither side said how many prisoners were released.

After the talks in Istanbul, both said it would involve more than 1,000 captured soldiers, making it the largest exchange of the three-year war.

The swap itself had appeared in jeopardy over the weekend, when Moscow and Kyiv traded accusations of delaying and thwarting the planned exchange.

Zelensky accused Russia on Sunday of playing a “dirty, political game” and of not sticking to the agreed parameters — to free all captured soldiers that are sick, wounded or under the age of 25.

Russia said Kyiv was refusing to take back bodies of dead soldiers, 1,200 of which it said were waiting in refrigerated trucks near the border.