Police in northern Italy on Thursday arrested six suspected extremists, including a couple with two children, who allegedly wanted to join militancy in Syria and Iraq, local media reported.

The couple's children, aged two and four, were entrusted to their grandparents after the arrests. The couple were residents of the northern city of Lecco.

Among the arrested was also a resident of the nearby city of Varese, a 23-year-old Moroccan who is the brother of a foreign fighter expelled from Italy last year and allegedly killed in Syria. The arrested Moroccan was set to travel to the conflict zone with the couple, investigators said.

Arrest warrants were also issued for a fugitive couple, 31-year-old Moroccan, Mohamed Koraichi, and his Italian wife, Alice Brignoli, 39, who had changed her name to Aisha after conversion to Islam.

Weeks ago, the family, also residing near Lecco, was reported by Italian media as being missing since last year when Brignoli's mother reported the disappearance to police. Later, investigators found the family had left Italy to join the Islamic State (IS) in Syria.

It emerged from wiretaps that Koraichi had talked in a phone conversation with one of the arrested about planning terror attacks in Italy, namely in Rome, investigators told a press conference in Milan on Thursday.

A relative of Koraichi, who had allegedly put him and his wife in contact with the aspiring jihadists, was also arrested in Thursday's operation.

The arrests took place during joint raids conducted by various police units.

Italian Prime Minister Matteo Renzi and Interior Minister Angelino Alfano praised the operation. "The arrested had evil intentions, they were assessing the possibility of carrying out attacks in Italy," the latter said.

Italy has toughened anti-terrorism measures and expelled dozens of suspects following the deadly attacks in Paris and Brussels.

Based on a law introduced last year, those found guilty of trying to go abroad to join IS or recruiting other foreign fighters face a sentence of up to eight years in jail which increases to up to 10 years for "lone wolves" who train in Italy with the goal of carrying out terror attacks here.