MADRID, September 3, 2008 (AFP) - Police have detained three men in Peru who are suspected of seeking to extort money from Spanish businesses in the name of Basque separatist group ETA, Spanish police said Wednesday.

The Peruvians, who are not members of ETA, which has killed 823 people in its 40-year campaign for an independent Basque homeland, were detained by Spanish and Peruvian police in Lima, the Peruvian capital.

The three men are suspected of sending threatening messages to more than 50 Spanish firms demanding the payment of 3,000 euros (4,360 dollars) in the name of ETA, police said in a statement.

The letters contained insults and sometimes photographs of bodies, it added.

ETA's main source of funding for its activities, including weapons purchases, renting of safe houses and payment of salaries for its members, comes from a so-called 'revolutionary tax' which it demands of businesses in the Basque region and neighbouring Navarra in Spain.

Spain officially recognises three Basque provinces: Alava, Guipuzcoa and Vizcaya. A fourth neighboring province, Navarra, is of Basque heritage.

Separatists consider these four provinces plus three in southwestern France -- Basse Navarre, Labourd and Soule -- as the Basque country.