Italy's capital has been rattled by increasing militancy by the extreme right since October, with weekly demonstrations by the neo-fascist youth group Blocco Studentesco often ending in clashes with police.

Local media initially blamed Thursday's attack on hard-core fans or 'ultras' supporting Lazio, who Tottenham had travelled to the capital to play in the Europa League.

But two supporters of AS Roma, Lazio's bitter city rivals, were among the 15 detained for alleged involvement in the mass attack on a downtown bar, suggesting a possibly different motivation.

Tottenham have a large contingent of Jewish fans and witnesses told Italian media that masked men armed with knives and baseball bats shouted "Jews, Jews" as they laid siege to a pub where the Tottenham supporters were drinking in a district popular with tourists in an old quarter of Rome.

Ten people were injured in the attack, which left 25-year-old English fan Ashley Mills in a serious condition. He underwent surgery for a severed artery in his leg on Friday and was being monitored by doctors, the Rome hospital where he is being treated said.

Lazio issued a statement on Thursday saying any suggestion that the assailants were Lazio supporters was "totally groundless".

Israeli ambassador to Italy Naor Gilon told reporters the attack on Spurs supporters, stemmed from "a new trend of anti-Semitism in Europe".

The World Jewish Congress called on Friday for Lazio to be suspended from European soccer if they failed to take action against hard core anti-Semitic supporters.

Media reports said Lazio fans chanted "Juden Tottenham, Juden Tottenham" at the match on Thursday.

DANGER TO JEWS

The violence has sparked a row about the safety of Jewish people in Rome.

The head of the city's Jewish community, Ricardo Pacifici, said the attack showed Jews were not sufficiently protected.

Police commissioner Giuseppe Pecoraro rejected the accusation, which he called a provocation.

"The police do more for the Jewish community in Rome than anywhere else in the world," he said.

Rome mayor Gianni Alemanno announced 21 million euros in funding for a Holocaust Museum "to give an immediate response to the many signs of anti-Semitism that have occurred recently in our city".

Alemanno is himself a former neo-fascist youth leader who was greeted with fascist salutes and cries of "Duce! Duce!" - the term adopted by Italy's dictator Benito Mussolini - when he was elected mayor in 2008.

The European far right has gained increased support as the continent's economic crisis has deepened, especially in the debt-laden south. Its most startling rise has been in the worst hit country, Greece, where the anti-immigrant Golden Dawn group has flourished.

Italy is no stranger to the trend.

Last week police arrested four people for allegedly inciting racial hatred through the website of the white supremacist movement Stormfront, confiscating a variety of weapons and neo-Nazi propaganda, after the group published a list of prominent Jewish citizens.

Teenagers carrying neo-fascist flags stormed a high school last month, tossing smoke bombs into classrooms as lessons were being taught, in a raid interpreted in Italy as an attempt by Blocco Studentesco to assert control over its turf.

Shortly afterwards a school due to host a meeting with local authorities about the "neo-fascist resurgence in schools" was daubed with swastikas, Celtic crosses and the word 'Hitler'.

There is no suggestion the Blocco is linked to the attack on the Tottenham supporters.

"We are proud to be fascists," the 18-year old Rome leader of the Blocco recently told Reuters in a suburban cafe, where swastikas had been scrawled across walls and furniture.

The movement venerates 1930s Italian dictator Mussolini but says it does not agree with his racial laws, which stripped Jews of Italian citizenship and barred them from holding government positions in 1938.

RACIST CHANTS

Israeli flags are a common sight among Tottenham supporters at matches, and fans refer to themselves in chants as the 'yid army'.

Lazio have long had fans with extreme right-wing sympathies, notorious for making Nazi salutes, unfurling anti-Semitic banners and chanting racist insults against black players.

At the game on Thursday, which ended in a goalless draw, Lazio supporters unfurled a banner reading 'Free Palestine'.

The English Football Association plans to send a report to European soccer's governing body UEFA following alleged anti-Semitic chanting by Lazio fans during the match on Thursday. Spurs manager Andre Villas-Boas has demanded an investigation.

Lazio was fined 40,000 euros for racist chanting against black players in another match against Tottenham in London in September. (Reporting by Naomi O'Leary; editing by Barry Moody/Mark Meadows)

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