The UN has urged Poland to end double standards in the way it treats migrants.
It says Warsaw welcomes Ukrainians but routinely locks up people from the Middle East or Africa who enter the country illegally from Belarus.
The special rapporteur for migrants’ rights, Felipe Gonzalez, said migrants and asylum seekers entering Poland illegally were often locked in foreigner centres without the right to leave while their asylum application was processed.
Mr Gonzalez said children and other vulnerable individuals should not be locked up merely due to their migration status.
According to the UN, 1.25 million Ukrainian refugees have registered for temporary protection in Poland. Many are being housed in private homes.