President Trump tweeted praise to Russia and Ukraine for Saturday’s prisoner swap that could herald an easing of tensions between the neighboring nations.

“Perhaps a first giant step to peace,” Trump posted. “Congratulations to both countries!”

Each country released 35 detainees in the exchange, the first in two years.

The group that returned to Ukraine included all 24 of the Ukrainian sailors who were captured by Russia during a naval confrontation last year in the Sea of Azov, as well as a filmmaker who was accused of planning a terrorist act against Russia.

Russia’s freed prisoners included Vladimir Tsemakh, a suspect in the downing of Malaysia Airlines flight MH17, a 2014 crash over eastern Ukraine that killed 298 people.

Ukraine and Russia have been locked in bitter conflict since 2014, when Russia annexed the Ukrainian province of Crimea.