The United Nations refugee agency is interviewing about 650 Sudanese migrants arrested by Egyptian police in a violent operation last week.
The UNHCR says some of those arrested did have refugee status
Egypt wants to deport them, as many have been refused refugee status.
But the UNHCR is speaking to them all individually to see whether any are refugees and so should not be deported.
Some 27 people died when police broke up a protest camp in Cairo last week. The Sudanese had been asking the UNHCR to send them to Western countries.
The UNHCR says the Egyptians have given it an extra week to complete the process after initially saying they must be deported by Saturday 7 January.
A spokeswoman told Reuters news agency that some of those interviewed were refugees, while others had had their claims rejected.
The UNHCR called on the Egyptian authorities to free immediately those registered as refugees.
South Sudan warning
The migrants had been camped outside UN offices since September, saying they faced discrimination in Egypt.
Thousands of police wielding truncheons and firing water cannon at protesters stormed the camp before dawn.
Meanwhile, the government of south Sudan has urged all Egyptians to leave the region, reports the AFP news agency.
Information Minister Samson Kwaje said they could return after passions aroused by the killings in the area had subsided.
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.