According to reports, Spanish police have found a video warning Madrid to withdraw its troops from Iraq and Afghanistan within a week.
The alleged footage was found in the wreckage of an apartment where Islamic militants blew themselves up at the weekend.
Meanwhile, Spain has drafted some 100,000 security personnel to monitor transport links and strategic sites, including nuclear reactors and reservoirs, over the holiday weekend.
Security has also been tightened on the Madrid and Barcelona metros, and at main airports.
The clampdown follows indications that the men said to be behind last month's Madrid bombings were planning new attacks during the Easter holiday, with one target a major shopping centre.
The suspects had targeted a shopping centre in Leganes, the southern suburb of Madrid where six of them blew themselves up during a massive police stakeout last weekend.
A judicial source said money, maps and explosives were found in the rubble of the apartment building in Leganes where the men were hiding out.
The newspaper 'El Mundo' said at least two bombs ready for detonation were found in sacks in the rubble, adding that the bombers wanted to strike during Easter week.
