India, Oct. 9 -- When Colombian President Gustavo Petro took to social media in May to declare that 7,000 of his compatriots were fighting and dying "without cause" in Ukraine, he was giving political voice to a grief that dozens of Colombian families had already been living privately for months.

That grief has now broken into the open again. The mother of a slain Colombian fighter has alleged that her son was recruited with false promises of high pay, had his passport confiscated on arrival, and that Colombian nationals serving in Ukrainian ranks are being held against their will and could be killed if they attempt to flee - claims relayed by Ruptly, a video agency operated by Russia's state broadcaster RT.

The allegations, which could...