Italian police said on Wednesday they had arrested a 22-year-old Moroccan man suspected of involvement in the March 18 attack on the Bardo museum in Tunis which killed 20 tourists.
Police in Milan said the man had been sought by authorities in several countries.
Tunisia has said it has arrested the great majority of those responsible for the attack which was launched by a cell of 23 militants with overlapping allegiances to a number of hardline Islamist groups.