Hundreds of asylum-seekers and would-be immigrants burst out of an Italian reception centre on the island of Lampedusa on Saturday and marched to the town hall, a day after the U.N. criticised conditions at the camp. Police said the group forced open the gates of the camp and marched peacefully to the town centre to protest against their detention. They were joined by a few hundred locals who also want the inmates transferred to bigger camps elsewhere in Italy.

But the interior ministry said there had been "no escape of illegal immigrants" because it was a camp for assistance rather than expulsion, "so there is no obligation to stay there". Many were already returning to the camp, it said in a statement.

The U.N. High Commissioner for Refugees (UNHCR) made a rare criticism of Italy on Friday, expressing concern about the camp where Italy holds people picked up or rescued trying to cross the Mediterranean from North Africa in small boats.

The UNHCR said it is only built for 850 people but now has up to 2,000 crammed in, many sleeping under plastic sheets. The Italian government says there are currently 1,300 residents.

Originally a temporary stop for people waiting for transfer to other centres in Italy, the camp's role has changed this year with tough new immigration rules meaning all those rescued are kept in Lampedusa until being granted asylum or expelled.

Many locals are opposed to Italian government plans to build a new camp to identify and expel illegal immigrants, which they say would turn the island into a "sort of prison" rather than a humanitarian centre for refugees rescued from the sea.

Mayor Bernardino De Rubeis, who leads opposition to the new camp, urged protesters to return, saying: "Only if you return peacefully to the centre can you be transferred out of here."

Prime Minister Silvio Berlusconi, who has introduced tough immigration rules that speed up expulsions, said "the people of Lampedusa can be calm because the situation is under control".

"This situation does not depend on the government but on the fact that Lampedusa is the part of Italy nearest to Africa," the centre-right premier told reporters.

About three-quarters of migrants reaching Italy by sea last year applied for asylum, of whom half got refugee status or protection on other humanitarian grounds, the UNHCR said.