Italian police have carried out what they termed a preventative operation against international terrorism involving 161 immigrants.
More than half of the immigrants, who are mainly Moroccans, have been taken in for questioning and have had their homes searched.
The police said the immigrants were suspected of having links with Islamic extremist groups.
Police in more than 30 Italian provinces took part in the operation.
Some of the immigrants who were found to be without work permits are to be expelled.
Italy's Interior Minister, Giuseppe Pisanu, said the objects of the raid were suspected on the basis of consistent evidence to be involved with Islamic extremist groups.
He stressed that ordinary hard-working Muslims in Italy had nothing to fear.
Among those detained were migrants who had been the subject of past probes into terrorist activity.
Security around possible targets in Italy has been stepped up ahead of Easter, which the secret services consider a particularly risky period.