Islamic extremists suspected over a bomb attack in a Pakistani market that killed more than 100 people had also planned an attack against the Vatican in 2010, Italian prosecutors said.
Wiretaps indicated the suspects were planning a bomb attack at the Vatican and that a suicide bomber had arrived in Rome, prosecutor Mauro Mura told a press conference in Cagliari, Sardinia.
Italian police have mounted a "vast anti-terrorist" operation against a group reportedly inspired by al Qaida.
Reuters report that the organisation wanted to support attacks against Pakistan's government and US forces in Afghanistan.
A police official said that most of the 18 arrests were centered on the island of Sardinia, but the operation covered seven Italian provinces.
Some arrests have been made, but the operation is still "ongoing", the official said.
The police say that some of those under investigation were believed to be involved in attacks in Pakistan, including one that killed more than 100 people in a market in the northwestern frontier city of Peshawar in 2009.
The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.