A Spanish man carrying potentially explosive substances and a bomb-making manual was arrested in Madrid, police said Tuesday.
Maps and plans for different sites in the capital were found in the suspect's possession, police said.
The 48-year-old man, identified only as Alberto R. M., was staying at a downtown Madrid hostel, whose manager notified authorities that he was acting suspiciously.
Officers found documents about explosives and various quantities of potassium nitrate, sulfur and coal powder, with some of the substances mixed in a 1.5-liter bottle.
The establishment was placed under surveillance and officers spotted an individual "who may have his mental faculties altered," police said.
The substances found and the mixture discovered in the suspect's room are being analyzed to determine if they could cause an explosion.
The suspect had instructions for making gunpowder and a manual called "Bombs and Homemade Explosives," as well as plans and notes on different sites in the Madrid area.
The addresses and telephone numbers of the U.S., Chilean, Uruguayan, Paraguayan and Brazilian embassies had been written down by the man.
The suspect has been charged with one count of possessing substances used to make explosives.
The man was arrested just days after police in Palma de Mallorca detained Jose Manuel Morales, a 21-year-old who was allegedly planning a massacre at the University of the Balearic Islands.
Morales spoke of his "complete admiration" for the two teenagers who killed 13 people on April 20, 1999, at Columbine High School in the U.S. state of Colorado.
He was arrested with 140 kilos (308 pounds) of explosives and told police that he planned to set off bombs at the university.
Eric Harris and Dylan Klebold gunned down 12 of their classmates and a teacher before turning their guns on themselves at the Colorado high school. EFE