The agency is calling on Kyrgyzstan not to send any more Uzbek asylum seekers back until it is known whether or not they are refugees.
Rupert Colville is a spokesman for the UNHCR in Geneva. He said: "We are strongly urging everyone in the central government and local authorities not to let it happen with any of the other asylum seekers."
Human rights defenders fear the four could be tortured in Uzbekistan where authorities continue to investigate the causes and organizers of the violence.
The Uzbek government says the May 13 violence left 173 people dead, while rights groups and opposition parties say up to 1,000 may have been killed.
(Reuters, RFE/RL's Uzbek Service)