Tens of thousands of Italian anti-war demonstrators marched through central Rome amid tight security to protest President Bush's visit, many waving peace banners and calling for the pullout of Italian troops in Iraq.

A small group of hooded protesters clashed with police, but the scuffles appeared to break up after a few minutes. It was unclear if anyone was injured.

Italy deployed about 10,000 police officers to protect Bush and his entourage. Premier Silvio Berlusconi (search) has said he is worried about the possibility of violence, and the U.S. Embassy warned Americans to avoid the crowds.

Most Italians opposed the Iraq war. Berlusconi, however, insisted that the cause was just, and his government sent 3,000 troops to help rebuild Iraq after Saddam Hussein's ouster.

"The war in Iraq was launched on the basis of mistaken assumptions and it's useless that Italy, with its little contingent, be there at America's side," said Luca Galassi, a 33-year-old student with a rainbow-colored peace flag around his waist.

The main protest drew 150,000 people, according to organizers. Police put the crowd at around 25,000.

Smaller demonstrations took place elsewhere in the capital. Some protesters shot fireworks at an Italian air force building and blocked roads around the city, but police did not intervene.

Bush arrived Friday to mark the 60th anniversary of the Allied liberation of Rome and to meet with Italian leaders and Pope John Paul II (search). He was to leave Saturday for Paris.

Critics questioned whether Americans should still be called "liberators" decades after World War II.

"Their credit as liberators was lost in Vietnam," 40-year-old Mario Bucci said.

Many leaders of the center-left opposition, who strongly opposed the Iraq war have urged protesters to demonstrate peacefully, stressed their gratitude for the U.S. role in liberating Italy.

"It's difficult to forget that the world would be different if 60 years ago, this great international alliance of forces hadn't formed against Nazism," said Romano Prodi, the European Commission (search) president and a top opposition Italian leader, who visited an Allied cemetery outside Bologna.

The area around Villa Taverna, the U.S. ambassador's residence in a posh neighborhood where Bush is staying, was cordoned off to traffic Friday morning. Hundreds of police were on alert near the Vatican, where the president met John Paul, and anyone entering St. Peter's Square had to pass through metal detectors.

Manholes were sealed and trash bins and cars removed along the routes the president would travel. Helicopters hovered overhead, and the airspace over Rome was closed to private aircraft. Some bus routes were suspended, selected roads were closed to traffic and the city center was largely quiet, with many staying home, while some schools and a few shops were closed.

In the past, some large demonstrations in Italy have turned violent, notably the 2001 Group of Eight summit attended by Bush in Genoa during which a 23-year-old protester was killed.