Italian anarchist Cospito, 55, has been on a hunger strike for more than 100 days to protest against being jailed under the strict 41 bis isolation regime.

"We are raising security in all of our embassies and consulates because at the moment international anarchists are mobilised against the Italian state," Tajani told a news conference in Rome.

In December, a Greek anarchist group claimed responsibility for an arson attack outside an Italian diplomat's home, calling it an act of solidarity with Cospito.

Tajani called it the most serious incident to date, but reported that numerous other attacks, acts of vandalism and demonstrations have taken place since November.

He said they believe the network includes both Italians and anarchists from other countries acting in concert.

Tajani referred to graffiti scrawled in Catalan on the building housing the Italian consulate in Barcelona.

Italian embassies, consulates or culture institutes have been targeted in Bolivia, Chile, Argentina, Brazil, Spain, Germany and Switzerland, he said.

On Monday, Cospito was moved from a prison in Sardinia to one in Milan with better healthcare facilities, as requested by Italy's ombudsman for prisoners.

The prisoner, who has lost more than 45kg and is reportedly so weak that he struggles to walk and keep warm, is surviving on water, sugar and honey.

Cospito is serving a 10-year sentence for shooting a nuclear energy manager for a state-controlled company in the leg in 2012 and 20 years for a series of dynamite attacks in Italy.

Prime Minister Giorgia Meloni's government has ruled out easing his detention regime, saying it cannot give in to threats or acts of terrorism.

The 41 bis, normally reserved for top Mafia bosses, is designed to prevent inmates from communicating with affiliates outside.

Cospito was placed under the regime in May, after he wrote articles from prison calling on fellow anarchists to continue their armed struggle.

Cospito has been sentenced to 30 years' imprisonment but prosecutors have appealed for it to be made a life term, with no parole possibilities.

Meanwhile, in Italy the threat of a major terrorist attack in Bologna linked to the Cospito case was made in an anonymous phone call to the reception of the Resto del Carlino on Tuesday, the daily newspaper said on Thursday.

The DIGOS special operations unit of the police spoke to the employee who took the call and are investigating to trace where it came from.

In other related news, Turin and Piedmont prosecutor general Francesco Saluzzo has come out against ending Cospito's 41 bis prison regime, in the official's highly anticipated recommendation to Justice Minister Carlo Nordio, well-informed sources told ANSA Thursday.

An opinion against the revocation of Cospito's 41 bis sentence was given to the Ministry of Justice by Saluzzo, they said.

The document also contains references to the need to constantly monitor the prisoner's health conditions.

Cospito's lawyer said on Thursday that his client was at a critical threshold but determined to press ahead with his hungers strike whatever the possible irreversible repercussions.

"Alfredo is getting thinner and thinner, he has lost 45 kilos," his defence attorney, Flavio Rossi Albertini, said after meeting his client in Milan's Opera prison, where he was moved due to its better health facilities compared to his original jail in Sassari.

"The situation is becoming extremely complicated and he is going beyond the critical threshold.

"He is absolutely determined to go on, but is aware that this will lead to irreparable consequences."

Also on Thursday evening, the hearing at the Supreme Court of Cassation on the petition filed by Cospito's defence counsel after the rejection of the complaint against the 41 bis declared by the Rome Supervisory Court was brought forward to February 24, defence sources said.

Cospito's partner Anna Beniamino, meanwhile, has suspended her own prison hunger strike to allow the complete focus to be on his struggle.

Beniamino has stopped refusing solid food at Rome's high-security Rebibbia Prison after 37 days of a hunger strike to raise awareness about her partner's campaign.

"I've reached my objective, to get people talking about Alfredo Cospito's condition," she said.

"We mustn't lower our guard on detention conditions. Ours is a battle for all."

ANSA, AP, AAP