The UN refugee agency visited an Egyptian detention centre holding Eritrean asylum seekers on Monday for the first time since February, after reports that Egypt had started a large-scale operation to send them home.

Officials from the office of the UN High Commissioner for Refugees (UNHCR) went to the centre in the southern town of Aswan to pave the way for a larger mission to find out whether the Eritreans should qualify for refugee status.

"They were able to see some of the asylum seekers. They are trying to prepare logistics for a UNHCR team that will go in the next few days to do refugee status determination," said UNHCR regional spokeswoman Abeer Etefa.

Eritreans arriving in recent months include Pentecostal Christians fleeing religious persecution and others trying to avoid military conscription, activists say.

UNHCR has the names of 1,600 Eritreans held by the Egyptian authorities for entering the country illegally, but rights group Amnesty International says Egypt may already have deported up to 700 of them this month.

Egypt has not confirmed any recent deportations and Etefa said UNHCR could not be sure that any had in fact left.

Some of the Eritreans may have been moved to Cairo or to military areas in other parts of Egypt, one activist said.

Etefa said another UNHCR team would leave for the Red Sea town of Hurghada on Monday evening to visit other centres where the Egyptian authorities are holding Eritrean migrants.

The Egyptian government has dismissed criticism of its treatment of the Eritreans, saying Egypt fulfils all its international obligations towards refugees. Under international humanitarian law, governments should not repatriate refugees who have a well-grounded fear of persecution if they go home.

UNHCR said some Eritreans appeared to have come to Egypt in hope of reaching Israel, but it also cited a deteriorating human rights situation in Eritrea. Activists say others had spent time in neighbouring Sudan but no longer felt safe there.