Migrants are transferred to another immigration centre by a ferry boat on the southern Italian island of Lampedusa February 20, 2015. REUTERS /Alessandro Bianchi

ROME (Reuters) - A group of migrants set fire to a shelter on the Mediterranean island of Lampedusa on Tuesday that caused no injuries, an Italian fire official said, marking an increase in tensions in Italy’s packed centers as arrivals continue.

Lampedusa’s mayor, Giusi Nicolini, said one building was set ablaze and the four men suspected of lighting it had been identified. Several mattresses were set on fire, but the extent of the damage was not yet determined, a fire department spokesman said.

Two other times, in 2009 and in 2011, fire destroyed portions of the migrant center, which has been the first port of call for tens of thousands of boat migrants sailing to Europe from Africa.

In the past two years, more than 320,000 boat migrants have arrived on Italian shores and many made their way north, bypassing European Union rules.

So far this year, more than 31,000 have arrived and Italian shelters are bursting at the seams even before the expected summer surge.

There have been other migrant protests in recent months against the Lampedusa shelter and EU asylum rules.

The island center is a so-called “hot spot,” where EU and Italian officials work together to identify and fingerprint asylum seekers before they are moved to the mainland.

European law says migrants must stay in the country where they first enter the bloc, and that is determined by where they give their fingerprints, prompting protests by asylum seekers who do not want to stay in Italy.