Almost 9,000 arrived in a single 40-day period between July 1st and August 10th this year, Angelino Alfano told reporters.
Despite the wave, illegal immigration had not yet become an "unmanageable situation", he said, as Italy struck a delicate balance between its duty to legitimate asylum seekers and the right to secure its borders.
Three boats carrying a total of 280 immigrants from sub-Saharan Africa were rescued overnight on Wednesday in the Mediterranean Sea between Sicily and Tunisia.
Taking advantage of calm waters, the influx has intensified in recent weeks, especially in Sicily and Calabria in the south.
In July, Pope Francis visited Italy's southernmost island of Lampedusa on his first trip outside Rome to mourn the thousands of migrants who have died crossing the Mediterranean, often in tiny vessels unsuited to such journeys.
Lampedusa is a common point of entry for illegal immigrants.