Quoting Italian investigators on Wednesday, Corriere said a suspected planner of the Madrid bombings in March - among those arrested on Tuesday - had intended to travel from Italy to Belgium possibly to take part in an attack on a "symbolic" target.
Rabai Uthman Said Ahmad, known as "Muhammad the Egyptian", was seized on Tuesday with a fellow suspect in Milan, and Belgian police, acting on information from Italy, arrested 15 people they said had been gearing up for an attack.
Italian Interior Minister Giuseppe Pisanu said on Tuesday that Ahmad was part of a "dangerous group of terrorists close to al-Qaida" which had been planning attacks.
Corriere said Italian investigators believed the symbolic target might have been the headquarters of NATO in Brussels or the European Parliament, which has its main building in Strasbourg, France, and offices in Brussels.
Investigators in Milan and Brussels were not available for comment.
The newspaper quoted Belgian prosecutor Daniel Bernard as saying he believed the suspects arrested in Belgium were probably planning an attack outside the country.
'Only one solution'
Corriere published excerpts from telephone conversations intercepted by police in which Ahmad purportedly urged others to carry out attacks and claimed responsibility for organising the Madrid train bombings which killed 191 people.
"We young people must be the first ones to sacrifice ourselves ... because God puts us all to the test, he tires us out, he tests the faith of us all," Ahmad was quoted as telling the man arrested with him in Milan on Tuesday.
The Madrid bombing's alleged key
planner has been arrested in Italy
"There is only one solution, to join al-Qaida," he was quoted as saying.
In another phrase, Ahmad was reported to have said: "The attack in Madrid was a project of mine and those who died were my most dear friends."
Spanish authorities have linked Ahmad to Serhane bin Abd al-Majid Farkhat, known as "The Tunisian", whom they consider the ringleader of the Madrid bombings.
Farkhat, 35, was killed on 3 April when he and six other suspects blew themselves up in a suburban Madrid apartment rather than surrender to police who had surrounded them.
In the phone-tap excepts published in Corriere, Ahmad also referred to some people leaving for Iraq for attacks.