The crowds, backed by demonstrators in boats, marched on US base Roosevelt Roads demanding that the navy stops using the island of Vieques for live firing.

News agencies reported that the crowds, including supporters of moves to make Puerto Rico a full US state rather than just a commonwealth, waved flags and chanted slogans accusing the navy of criminal behaviour.

In the Puerto Rican capital San Juan, officials said that the island's residents were paying a high price.

War games: Vieques used since Second World War

Norma Burgos, Puerto Rico's secretary of state, said: "The American citizens who live in Vieques have the same right as Americans anywhere else to peace and welfare.

"We have contributed with our sweat and blood to the formation of this republic."

US forces based at the naval station have been using Vieques for target practice for around 50 years. The Navy owns two-third's of the island's 33,000 acres.

While residents have reportedly battled on and off against the US navy over the use of the island, matters came to a head in April when a civilian security guard on the island was killed by a stray bomb.

The navy later admitted that it had wrongly fired 267 radioactive shells at the island in February, further increasing tension over live firing.

The march, which saw pro-US politicians and independence activists united, followed the release last week of a report by the special committee on Vieques, a bipartisan group appointed by Governor Pedro Rossello.

The report accused the US Navy of having violated basic human rights by its continued bombing of Vieques.