Tens of thousands of people have gathered in the northern Italian city of Vicenza to protest a planned U.S. military base expansion nearby.

Special trains and buses have brought in protesters from all over Italy to take part in the march Saturday.  Leftists and green parties, pacifists, anti-globalization activists and local residents are expected to participate.

More than 1,000 police and several helicopters are in place along the march route. 

The U.S. Embassy in Rome has advised Americans to avoid traveling to the area.

The Vicenza City Council approved the extension of the U.S. base in a new location at the Dal Molin airport.  The project would almost double the U.S. military presence in the Vicenza area.

Prime Minister Romano Prodi said last month that he would not oppose the plan.

He has called on activists to keep the rally peaceful.

Some 20,000 people in Vicenza protested the base expansion in December.

Some information for this report was provided by AFP and AP.