Tens of thousands of people from across Italy converged on the northern city of Vicenza on Saturday to protest against the expansion of a US military base.
Organisers said more than 100,000 protesters took part in the colourful, festive demo. Police officials said the number was around 70-80,000.
The demonstrators wound their way through the streets of the city, covering 6.5 kilometres in all, waving rainbow peace flags and banners bearing slogans against Premier Romano Prodi's government and the American government.
The demo went smoothly despite initial fears that there could be scenes of violence or clashes with the police, who numbered more than 1,500.
Before the march started, Prodi appealed to the demonstrators to refrain from violence.
"Demonstrations are a fundamental part of democracy but they must be peaceful, calm and without violence," the centre-left chief said in a radio interview.
Interior Minister Giuliano Amato thanked the protesters afterwards for "demonstrating peacefully and helping to prevent the risk of infiltration (by violent fringes)".
A so-called red zone was set up around the historic centre where most of the city's monuments are situated and which was off-limits to the protesters.
The United States embassy in Rome advised Americans in Italy to avoid Vicenza and the base so as not to become "targets for anti-American protestors".
Many of the protesters were local residents fearful that an enlarged base will strain the city and its resources and possibly make it a target in the event of a military conflict or terrorist attack.
Other groups against the base include pacifists, environmentalists, anti-globalisation activists, trade unions and several parties in Prodi's own nine-way coalition.
Nobel Prize-winning playwright Dario Fo and his wife, Senator and actress Franca Rame, were among the protesters.
Opposition chief and former premier Silvio Berlusconi blasted the protest as "anti-American".
"I am very sad... because thousands of protesters are marching in Vicenza against the United States," Berlusconi commented from his home in Sardinia.
"We mustn't forget that many young Americans died in Italy for our freedom (during World War II)," said Berlusconi, whose centre-right government gave informal consent to the expansion of the Vicenza base.
The old base currently houses some 2,750 troops.
The expansion project involves building barracks at Vicenza's Dal Molin airport on the other side of the city to accommodate 2,100 more US soldiers who are currently stationed in Germany.
Washington's aim is to unite its 173rd Airborne Brigade, which is divided at the moment between Vicenza and two bases in Germany. If Prodi had nixed the plan, the Vicenza base would have been shut down altogether and American troops transferred to Germany.
Prodi stressed on Saturday the importance of Italy's alliance with the US and NATO.
"I decided not to modify our 50-year-old defence policy... I have always said our foreign policy rests on three pillars - the United Nations, the European Union and NATO," said Prodi, who won last April's general election.
But Prodi's decision has dismayed three parties in his alliance - the Communist Refoundation Party (PRC), the Italian Communists' Party (PDCI) and the Greens.
These parties supported Saturday's protest, arguing that there should at least be a local referendum on the issue.
The parties' ministers and undersecretaries reluctantly agreed not to attend the rally so as not to create embarrassment for the government but party chiefs and a number of ordinary MPs took part.
PRC leader Franco Giordano, whose party is the third biggest in the governing coalition, urged Prodi to reconsider his decision on the base.
"I ask the government to listen to the motives of the protesters," he told reporters at the rally.
PDCI leader Oliviero Diliberto, who was also present, said that "Prodi has to take the pacifist population into account because a lot of them voted for him".
He nonetheless sought to play down divisions, saying that "the government certainly won't fall because of an American base".
The centre-right opposition made political capital out of the split, stressing that leftist and Green politicians were demonstrating against their own government.
Berlusconi's Forza Italia party called for Prodi's resignation, saying that "his own majority is against him and the government cannot muster support on its foreign policy".
Commenting on the rift on Saturday, Prodi admitted he was "unhappy" that several government parties had "a different opinion about the American base".
"But that does not break the government's solidarity," he added.
Defence Minister Arturo Parisi insisted that the government had "only the country's interests at heart".
"But the government is also aware of the heavy burden it is placing on the shoulders of the people of Vicenza," he said, stressing that the government would do everything possible to address the concerns of the local community.
Surveys show that some 70% of Vicenza residents are against enlarging the base.
Residents and environmentalists fear the impact on the city, which boasts a host of buildings and villas by Renaissance architect Andrea Palladino and is on UNESCO's list of World Heritage Sites.
The Vicenza council has thrown out proposals to hold a referendum on the base's fate even though local polls have shown that 84% of the city's 115,000 residents would like to have a say on the issue.
There have been repeated demonstrations by locals against the base expansion plan.
But there have also been smaller protests by those who argue that Vicenza's economy will suffer if the base is closed and that more than 1,200 locals who currently work at the base will lose their jobs.
