Egypt has freed most Sudanese women and children from among the hundreds of migrants arrested in a police operation in Cairo earlier this month.
The UNHCR says some of those arrested did have refugee status
At least 27 people died in a raid on a park, where many migrants, some facing deportation, were staging a sit-in.
Among the 233 released detainees were people from the war-torn Darfur region.
The United Nations refugee agency has said there have been no assurances from Egyptian authorities that the migrants would not eventually be deported.
Thousands of migrants, many of whom had been refused refugee status, had been camped in the park outside UN offices since September, saying they faced discrimination in Egypt.
They had been asking the UNHCR to send them to Western countries.
They were removed in a violent dawn raid by Egyptian police wielding truncheons and firing water cannon.
"We are extremely relieved that this group has been released, and an additional group of 39 - women, children and UNHCR card holders - will also be released today," said UNHCR official Radhouane Nouicer, AP news agency reports.
More than 220 of more than 600 people arrested remain in custody.
The UNHCR is speaking to them all individually to see whether any are refugees, who will then not face deportation.
The UNHCR has until 26 January to determine their legal status.
Millions of Sudanese fled a 21-year war between north and south.
The war ended a year ago but those in Egypt say it is not safe for them to return.
A separate war is still raging in the western region of Darfur.