The Basque separatist group ETA may try to attack the Americas Cup, which is nearing its climax in Valencia.

After ETA said its terrorist campaign would resume 'on all fronts', security at the America's Cup was reinforced.

Lengthy traffic jams built up outside Valencia's Port America's Cup as police officers carried out car by car searches and foot spectators were subjected to bag checks at the gates equipped with metal detectors and x-ray machines.

A significant number of Spain's Civil Guard and the city's local police were in evidence inside the port area.

"We are working in cooperation with the security forces of the State", tolf AFP Paco Latorre, communications director for ACM.

Security checks have been "intensified," sources close to the National Police confirmed to Spanish media.

Almost two million visitors have descended on the purpose built port in Spain's third largest city since the competition got underway in April where surveillance is extensive: on the water, underwater, in the air and on land.

Organisers had already announced stricter security measures for the three-month long yachting extravaganza than even were in place for the visit by Pope Benedict XVI to Valencia last year. The security operation features the deployment of 2000 police officers and security agents, 24 boats, five helicopters and 200 surveillance cameras.

Security had already been strengthened at the end of January following the arrest of a suspected ETA member in Catalonia carrying information on the America's Cup.