(GENEVA) - Ten United Nations human rights experts on Friday said they have written to the European Union expressing their concerns over the bloc's new rules on illegal immigrants.

"One principal concern relates to the detention regime pending removal procedures for irregular immigrants. The Directive envisages detention periods of up to 18 months, which appear to be excessive," said the experts in a statement.

The European Parliament on June 18 approved tough new rules on illegal immigrants, allowing detention for up to 18 months prior to expulsion.

Adopted in Strasbourg by 367 votes to 206 with 109 abstentions, the new rules focus on illegal immigrants -- visa-overstayers are the biggest category and estimated at some 12 million people -- but not refugees who want to seek asylum in Europe.

The experts said: "We have sent this letter to the French Presidency, and to all pertinent EU Governments, to express our concern regarding some of the provisions of the Directive as it currently stands."

Besides the length of detention, they also point out concerns that the new rules would allow EU states to detain vulnerable groups such as unacompanied children and people who have been trafficked into the bloc.

The experts stressed that "irregular immigrants are not criminals" and should not be subjected to detention.

"Member States are obliged to explore the availability of alternatives to detention and detention must only be for the shortest possible period of time," they said.

They also expressed concern on that illegal migrants who were subjected to forced expulsion could be banned from the bloc for up to five years, saying that it could impact on vulnerable groups such as victims of human trafficking.

"We believe that existing safeguards in the proposed text should also be reinforced with a view to facilitate full compliance with the principle of non-refoulement," they said.

They also asked the EU to enhance protection of rape victims and other victims of violence.

The experts include the UN Chairperson-Rapporteur on Arbitrary Detention Manuela Carmena Castrillo, the Special Rapporteur on the sale of children, child prostitution and child pornography, Najat M'jid Maala, and the Special Rapporteur on the human rights of migrants, Jorge Bustamante.

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