Although the agreement, forged on Thursday, May 22, stresses that detention "will only be permitted where other less coercive measures cannot be applied," it has nevertheless been criticized by pressure groups because it includes provisions allowing officials to extend the detention period for a further 12 months, for instance if the immigrant refuses to cooperate.

The debate on the EU's "Return Directive" comes at a sensitive time for Europe, with some governments seeking to crack down on the seemingly unstoppable flow of Africans and Asians who continue to enter their territories illegally.

This week, the conservative Italian government of Silvio Berlusconi launched a major anti-immigration push when it said it would join other European countries such as France in making illegal immigration a criminal offence punishable by jail. The move has infuriated another Mediterranean country, Spain, which fears that it will induce would-be immigrants coming from Africa to try and reach its territory instead.

Non-binding

Member states have been wrangling over the maximum period immigrants can be kept in detention for almost three years. Earlier this month, over 10 countries voiced opposition to a draft law.

The latest deal on the Return Directive was brokered by the Slovenian presidency of the EU and also regulates the deportation of illegal immigrants, re-admission to their country of origin and access by non-governmental organizations to EU detention centers.

The draft agreed by EU ambassadors on Thursday does not force governments to pay for an illegal immigrant's legal aid, as some had wanted.

Instead, it includes a non-binding invitation to governments to set aside the necessary funds needed to assist destitute migrants.

Opposition

The package will next month be voted on by the European Parliament. But its passage is threatened by reservations voiced by the second-largest political bloc in the parliament, the Socialists.

They say the six-month detention period is too long.

Further opposition has come from the non-governmental sector.

According to the European Council on Refugees and Exiles, detention should only ever be a last resort.

"We consider that systematic detention of people who have committed no crime, including families and vulnerable persons, is inhumane and unwarranted," the NGO has said.

This is the first time that the European Parliament has been given a decisive voice on immigration, an issue normally reserved to member states.