Spanish authorities said Tuesday that they had disrupted a plot by a cell of Islamic radicals to blow up a Madrid court complex that is the headquarters of the country's top anti-terrorism investigators and judges.

Police arrested eight suspects in six cities on Monday and Tuesday in an effort to break up the cell, which was composed primarily of people with criminal records, according to statements released by the Spanish Interior Ministry.

Interior Minister Jose Antonio Alonso said the suspects were planning an attack on the National Court building in Madrid and that "police are not ruling out other possible targets."

Authorities searched several locations across Spain but said they did not find any explosives or signs that an attack on the building was imminent. Investigators also said they found no evidence to suggest that the alleged plotters were connected to the commuter train bombings in Madrid in March that killed 191 people.

The Interior Ministry said the cell included four Algerians and one Moroccan. Some members of the group had been in touch recently with people in other European countries, as well as the United States and Australia, according to ministry officials, who did not elaborate.

The arrests appeared to be the result of a broad international investigation. Moroccan security officials received tips about the cell from an informant and passed the information to Spanish authorities, according to the Spanish daily El Mundo, which also reported that the suspects were planning to drive a truck filled with 1,000 pounds of explosives into the courthouse complex.

One of the cell's leaders was an Algerian man who has been imprisoned in Switzerland since September 2003 and is affiliated with the Armed Islamic Group, a radical organization that has been fighting the Algerian government for a decade, the news agency Europa Press reported.

The National Court building includes offices of judicial magistrates who oversee anti-terrorism investigations in Spain, including the probe into the train bombings and a separate long-running examination into al Qaeda networks in Spain.

Spanish investigators have been unable to determine who ordered the Madrid bombings but have detained 20 suspects -- most of them Moroccan immigrants -- accused of being affiliated with or inspired by al Qaeda. Seven other suspects killed themselves in an explosion in April after police surrounded an apartment building where they were hiding.

Also on Tuesday, a Spanish television station broadcast for the first time a security-camera videotape of the train bombings, the Associated Press reported from Madrid.

The video, aired by Telecinco, begins after one bomb has already exploded, with dazed commuters on a smoke-shrouded platform at the Atocha station. The time on the tape says 7:38 a.m. Then smoke flows toward the camera and people are knocked over -- apparently by another blast. Seconds later, flames erupt from a stopped train, filling the screen.

Four minutes after that, bodies are seen scattered on the platform amid puddles of blood as emergency personnel attend to them.