Italian forensic experts are set to start testing chemicals seized at a Perugia mosque suspected of terrorist activity.
Police arrested the imam of the mosque, Mostapha El Korchi, and two other Moroccan assistants on Saturday.
Among the chemicals seized were fertilisers, household chemicals, an anti-rust acid, a laxative and sleep medicine which police said could be mixed to make bombs.
They also seized films and computer files they said were used for combat training. Police said El Korchi had downloaded bomb-making manuals.
Maps with several northern cities including Milan circled were seized along with several photos of El Korchi arriving at Rome's Fiumicino Airport and maps showing aqueducts in the region around Perugia, Umbria.
Police said Monday the three men arrested had not carried out "specific, potential criminal actions" against the sites identified in the Perugia probe.
But they said "significant evidence" had emerged from other material seized.
El Korchi had been under surveillance for months with police tracking his Internet activity and recording public sermons in favour of jihad or holy war, police said.
The dawn raid on the mosque and reports of alleged terror plans alarmed Italy, which has not experienced the sort of Islamist militant attacks suffered by Britain and Spain.
Sunday newspapers described the mosque as a 'terror school' and said al-Qaida militants were "ready to strike".
In signs of a backlash, right-wing politicians called for the closure of Italian mosques until they were checked for illegal activity.
Members of the centre-left government rejected such calls on Monday and urged integration efforts to be stepped up.
Health Minister Livia Turco called for schools to train imams and a register of mosques along the lines of other countries such as France, "from which we have much to learn on these issues".
Milan prosecutor Stefano D'Ambruoso, a United Nations advisor on terrorism, warned that intensive checks on Muslim activities could backfire and disclosed that European mosques were already being monitored.
Worshippers at the Perugia mosque have called the accusations against their imam "absurd" and voiced confidence he will eventually be cleared.
There have been a number of terrorism trials in Milan which have resulted in convictions only for forging documents and favouring illegal immigration.
