Nigerian medical student Oduola Adebowale said he and some friends were trying to get on a train to flee Ukraine when the soldiers pointed guns at them and ordered them back.
The Ukrainian troops told him they were only letting pregnant woman on the service from the city of Lviv to the Polish border, but he said he saw them stop some pregnant African women from getting on board.
"When we asked why they were doing this, the soldiers pointed guns at us, endangering our lives," he told Reuters days later after he finally managed to complete his journey and landed at Nigeria's Abuja airport on Friday.
Scores of foreign students have echoed his complaints in social media posts, saying they were treated badly as they queued up with the crowds trying to escape Russia's invasion.
Reuters could not independently verify the accounts of Asian and African students being pulled off trains, held up at borders and pushed to the back of long lines.
Ukraine's national police and state border service did not immediately respond to requests for comment on reports that Reuters had received from refugees.
But the African Union said this week it was disturbed by what it had heard and the UN refugee agency said it had urged authorities in countries neighbouring Ukraine to open their borders to African citizens.
Ukraine's Foreign Minister, Dmytro Kuleba, said on Wednesday authorities had sent up a hotline for African and Asian students looking for help in getting out. "We are working intensively to ensure their safety & speed up their passage," he tweeted.
