At least one is said to have links to the Red Brigades, a left-wing group that carried out attacks in the 1970s.
Italy will host G8 leaders on 8-10 July in L'Aquila, Abruzzo region.
The city was badly damaged in an earthquake that shook the central region in April, leaving some 60,000 people homeless.
The meeting of the industrialised nations was first planned to be held on the Sardinian island of La Maddalena.
Italian Prime Minister Silvio Berlusconi shifted the venue weeks after the earthquake to focus attention and government resources on the disaster-hit territory.
Among those arrested was Ernesto Morlacchi, son of one of the founders of the Red Brigades, the French news agency AFP reported.
Material seized included a bomb in searches carried out in Rome, Milan and Genoa following a two-year investigation, local media reports said.
Six arrested in suspected plot to attack G8: Reports
ROME — At least six people have been arrested on suspicion of planning an attack on the Group of Eight summit next month in Italy, news reports said Thursday.
The six were arrested on Wednesday and accused of criminal association for purposes of terrorism and arms possession, one month ahead of the July 8-10 summit of leading industrialized nations, the ANSA news agency said.
The probe began two years ago when the summit was set to be held at the Sardinian island of La Maddalena, the reports said.
Italian Prime Minister Silvio Berlusconi made the surprise decision to move the G8 summit to L'Aquila some three weeks after the April 6 earthquake that claimed 295 lives to "show solidarity" with the victims.
Berlusconi argued that millions of euros could be saved by moving the venue to a modest site on the outskirts of L'Aquila, and that anti-globalisation activists would think twice before staging protests in a disaster zone.
Italian newspapers Corriere della Sera and La Stampa said the gang had shifted their target to the new venue.
Weapons seized included a bomb during searches carried out in Rome, Milan and Genoa following a two-year probe, the reports said.
La Stampa said police had made nine arrests.
Among those reportedly arrested was Luigi Fallico, who was close to the terrorist group the Red Brigades in the 1970s and accused of wanting to resume an armed struggle.
His name was cited in several investigations into the Red Brigades in the 1980s, ANSA said.
Also said to have been arrested was Ernesto Morlacchi, son of one of the founders of the Red Brigades, accused of the 1978 murder of Italian former prime minister Aldo Moro.
Five are in custody while a sixth is a minor and was placed under house arrest, ANSA said, adding that weapons were found at his home.
Rome police were to hold a news conference later Thursday.
© Copyright (c) AFP