Thirty-one children were reunited with their families in Ukraine this weekend after a long operation to repatriate them from Russia or Russian-occupied Crimea, where they had been taken from areas occupied by Russian forces during the war.

Mothers hugged sons and daughters as they crossed the border from Belarus to Ukraine on Friday after an arduous rescue mission that involved traveling through four countries.

Thirty-one children have returned to Ukraine after being illegally transported to Russia from territories occupied by Moscow, the NGO Save Ukraine announced today on social media. “Today we welcome another 31 children returning to their homes, who were illegally transported by Russians from occupied territories,” wrote Mikola Kuleba, an executive at the non-governmental organization.

These children had been taken to Russia from the regions of Kharkiv, in northeastern Ukraine, and Kherson, in the south, explained the organization, whose main mission is to combat the “displacement” of Ukrainians, as it describes it.

According to the NGO, the children carrying suitcases and bags crossed the border on foot on Friday, along with relatives, then boarded a bus to continue their journey.

Mikola Kuleba hailed the “heroic mothers” who went to collect their children and said it was the “hardest” mission the NGO had to carry out so far.

An elderly woman who was to bring back two grandchildren died from “stress,” Kuleba wrote on Facebook, explaining that the Ukrainian women were subjected to a “13-hour interrogation” by the Russian security services (FSB).

Kyiv authorities estimate that more than 16,000 Ukrainian children have been “abducted” and taken to Russia since the invasion of Ukraine began on February 24, 2022, and many have reportedly been given to foster families.

Moscow denies these claims, and says it has “rescued” Ukrainians by removing them from the fighting and is implementing procedures to reunite them with their families.

On March 17, the International Criminal Court issued a historic arrest warrant against Russian President Vladimir Putin, who is “allegedly responsible for the war crime of illegally deporting” Ukrainian minors “from occupied territories of Ukraine to the Russian Federation.”

The Hague-based ICC also issued an international arrest warrant for Maria Lvova-Belova, the commissioner for children’s rights in the Russian Federation, on similar grounds.