There have been violent clashes between riot police and demonstrators protesting against the planned extension of a US military base in Italy.
The latest protest over the Dal Molin project was planned to coincide with American Independence festivities and comes just days before a G8 summit opens in Italy.
Some 300 out of several thousand demonstrators hurled stones and bottles at police who replied with tear gas.
The extension plan was drawn up under the Bush administration. Its opponents say the arrival of Barack Obama has not changed anything.
A referendem showed locals did not want the deal which they fear will damage the environment and threaten the nearby renaissance town of Vicenza.
But authorities say it will create jobs and boost the economy.