But the agreement coincided with large-scale deportations of Eritrean migrants by the Egyptian authorities and it was not clear whether the United Nations will have time to save many of them from forcible repatriation.

Abeer Etefa, a spokeswoman for the regional office of the U.N. High Commissioner for Refugees (UNHCR), said senior UNHCR staff were leaving later on Sunday to visit detention camps in Aswan in southern Egypt and Hurghada on the Red Sea coast.

"We were told by the Ministry of Foreign Affairs that our staff is welcome to visit those detention centres," she said. UNHCR last had access to the camps on Feb. 27, she added.

Foreign Ministry spokesman Hossam Zaki said in a statement that the ministry would welcome meetings between UNHCR officials and the Eritreans to determine their status and rule on the applications for political asylum which some of them have made.

UNHCR has the names of some 1,600 Eritreans held by the Egyptian authorities for entering the country illegally, mostly with plans to move on to other countries, especially Israel.

The rights organisation Amnesty International says many of them could be at serious risk of torture if they go home.

Amnesty said last week 500 had already been flown to Eritrea. Another plane carrying 200 of them left on Saturday night, a rights activist added, quoting Egyptian officials.

Activists say the returns appeared to be the largest mass deportations of asylum seekers from Egypt in decades.

The Egyptian spokesman dismissed criticism of his government's treatment of the Eritreans, saying Egypt fulfilled 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.

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

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