The visit of Bush represents the evil image of the Empire

Adolfo Jimenez, union leader

Police estimate that about 3,000 people attended Sunday's rally - it was advertised on the internet and is expected to be followed by more protests.

On an official level, Mr Bush's visit has been welcomed. The BBC Madrid correspondent, Flora Botsford, says that as one of Europe's few conservative leaders, Prime Minister Jose Maria Aznar is unlikely to offer any real opposition to the American president's policies.

The two leaders are expected to discuss Washington's controversial plans for a missile defence shield, as well as issues relating to EU expansion and Nato, the environment, and investment in the Americas.

Myriad causes

"The visit of Bush represents the evil image of the Empire," union leader Adolfo Jimenez told the demonstrators gathered at the Puerta del Sol.

"We cannot but condemn the co-operation of the Spanish Government with the United States" by allowing American troops on Spanish bases he said.

Bush is preparing for his first trip to Europe since taking office

Police maintained a heavy presence as demonstrators also voiced their opposition to Mr Bush's environmental policies, the death penalty in the US, the arms race, globalisation and the failure to abolish Third World debt.

A feminist group carried a large banner that read: "What misfortune that the mother of Bush could not abort."

Other slogans read "Cowboy Attila" and "Bush Taleban".

Trade unions and other groups plan to confront Mr Bush when he arrives on Tuesday.

The US president is due to attend a Nato meeting on Wednesday and then join a summit of European Union leaders in Sweden on Thursday.

He is also to hold talks with the Russian President Vladimir Putin in Slovenia before returning home.