Suspected extremists being investigated in Italy over links to al-Qaeda may have been planning an attack on the Vatican in 2010, prosecutors say.

A militant ring was found to be operating in Sardinia, and there had been possible plans to target the Holy See, according to investigators.

Police issued 20 warrants and made nine arrests in raids on Friday.

Some of the suspects are believed to have organised the 2009 market bombing in Peshawar in Pakistan.

Local media said two of the men had provided protection for former al-Qaeda leader Osama Bin Laden.

Prosecutor Mauro Mura told a press conference in Cagliari, Sardinia, that wiretaps indicated the suspected terrorists had been planning a bomb attack at the Vatican in March 2010.

There had been "signals of some preparation for a possible attack", including the arrival of a suicide bomber in Rome, the Associated Press quoted Mura as saying.

"We don't have proof, we have strong suspicion," police chief Mario Carta said.

Police earlier said those arrested came from Pakistan and Afghanistan and the operation was ongoing.

The suspects were accused of staging attacks against the government in Pakistan.

More than 100 people were killed when a huge car bomb ripped through a busy market in Peshawar, Pakistan, in October 2009.