ROME - Decriminalizing cannabis sales would strike a blow against Islamic State militants and Italian mobsters who, according to ongoing investigations, are smuggling hashish together, Italy's top prosecutor told Reuters.The main smuggling route for North African hash - compressed cannabis resin - now runs from Casablanca, Morocco, through Algeria, Tunisia to Tobruk in eastern Libya, said national anti-mafia and anti-terrorism chief Franco Roberti.Along that route is the seaside city of Sirte, which now serves as a Mediterranean base for the most powerful Islamic State (IS) branch outside Syria and Iraq."Certainly IS controls the Libya route; it controls the coast along the Gulf of Sirte," said Roberti in his frescoed office in the 17th century building that once served as the Vatican prison.In investigations whose details have not yet been made public, police have found evidence that Italian organized crime, which has long controlled most of the country's illegal drug supplies, and "suspected terrorists" in North Africa are trafficking hash together, Roberti said."Decriminalization or even legalization would definitely be a weapon against traffickers, among whom there could be terrorists who make money off of it," he told Reuters.Citing estimates by the United Nations Office on Narcotics and Crime, Roberti said that the illegal drugs trade, which includes cannabis and hash, earns more than 32 billion euros ($36.10 billion) annually for Italian organized crime. Islamic State controls just a part of the North African route, but the narcotics trade as a whole provides just under seven percent of the group's funding, according to a report by analysis company IHS published on Monday.In his new book "Il contrario della paura" or "The opposite of fear", the 68-year-old Roberti writes at length about the similarities between Islamic militant groups and Italy's mafias, and he reflects on ways to improve the fight against both.Italy has not been attacked by Islamist militants, but IS propaganda films regularly mention Rome and the Vatican as possible targets. Many Italian sites are considered at high risk of attacks, Roberti said.Prime Minister Matteo Renzi's government gave Roberti's office, which has coordinated the national fight against organized crime since the early 1990s, the job of overseeing investigations into terrorism in February last year.Since then, Roberti and his team of experienced mob prosecutors have begun to add terror cases to a national database previously dedicated only to organized crime, he said.COSA NOSTRAOne reason it makes sense for his office to coordinate anti-terror investigations is that Islamist militants and traditional mafias - like Sicily's Cosa Nostra - commit similar crimes, Roberti said."International terrorism finances itself with criminal activities that are typical of the mafia, like drug trafficking, smuggling commercial goods, smuggling oil, smuggling archaeological relics and art, kidnapping for ransom, and extortion," he said. Facing the huge challenges of fighting people smuggling, cocaine trafficking, and international terrorism, investigators are spending too much time and energy to combat cannabis dealers, and to little effect, said Roberti."We spend a lot of resources uselessly. We have not succeeded in reducing cannabinoid trafficking. On the contrary, it's increasing," said Roberti, who has been combating the mafia for more than three decades."Is it worth using investigative energy to fight street sales of soft drugs?" he asks. According to the most recent government data, about 3.5 million Italians between the ages of 15-64 used cannabis in 2014.Cannabis is much less damaging than hard or synthetic drugs, which should not be decriminalized, he said. But Italy's laws against selling or growing cannabis are severe and can lead to imprisonment.A bipartisan group of lawmakers proposed legalizing cannabis possession and cultivation earlier this year, but it is not supported by the leaders of any major parties.In his book Roberti suggests that all of Europe, and not just Italy, should be considering a better use of investigative resources: "On decriminalization (of cannabis), there should be an Italian domestic debate, but also a European one."