Authorities announced another arrest in the Madrid terror bombings Monday and sent police to patrol subway and bus stations, as a newspaper said a group linked to Al Qaeda (search) threatened to turn Spain into "an inferno."
Court officials said the arrest came Saturday in Ceuta, a Spanish enclave on the Moroccan coast. No details were given on the man's identity or possible role in the March 11 train attacks, which killed 191 people. Another suspect whose weekend arrest was also announced Monday has been released after questioning, officials said.
The arrest raises to 16 the number of people in custody, including six charged with mass murder.
Interior Minister Angel Acebes confirmed Monday that one of those killed in a homicide blast Saturday in an apartment south of Madrid was Moroccan Jamal Ahmidan (search), a prime suspect in the bombings.
At least five terror suspects are believed to have died in the explosion, along with a special forces officer. One of the suspected terrorists has yet to be identified. Sarhane Ben Abdelmajid Fakhet (search), a Tunisian believed to be the overall leader of the attacks, was among those killed, Acebes said.
A U.S. intelligence official said people should not think that the terrorist threat in Spain is over because of the arrests and deaths of the suspects in the train bombing.
"They have certainly made a lot of progress in rolling up those responsible, but you shouldn't assume that those people were the only ones of concern," the official said.
Fear of more violence prompted authorities to order police to patrol the city's subway and bus stations while civil guards and army units continued checking the country's rail system.
A subway station on a line leading to the airport stopped luggage check-in services as a precaution.
Acebes said police found 22 pounds of dynamite and 200 detonators in the apartment where the suspects blew themselves up. He said this indicated they were plotting more violence, and that the brand of dynamite and the detonators linked them to Friday's failed attack on a high-speed rail line south of Madrid.
The newspaper ABC reported that hours before the terrorists killed themselves Saturday, it received a fax from the group that had claimed responsibility for the March 11 bombings. This time, the group warned it would turn Spain "into an inferno" unless the country withdrew its support for the United States and pulled Spanish troops from Iraq and Afghanistan, ABC said.
"If these demands are not met, we will declare war on you and ... convert your country into an inferno and your blood will flow like rivers," the letter said.
It gave Sunday, April 4, as the deadline for compliance.
ABC said the letter was handwritten in Arabic and signed "Abu Dujana Al Afgani, Ansar Group, Al Qaeda in Europe." A videotape found outside a Madrid mosque March 13 showed an Arabic-speaking man reading a statement signed by Al Afgani in which he claimed responsibility for the train bombings.
The Interior Ministry said officials "attach a certain credibility to the authorship (of the letter), but not to the threat" contained in it.
ABC quoted unidentified sources in Spain's National Intelligence Center as saying the language used in the letter was similar to that in the video.
"Ansar Group" appeared to refer to Ansar al-Islam, an Islamic guerrilla group blamed for terrorist strikes in Iraq, Jordan, Turkey and Morocco.
French private investigator Jean-Charles Brisard says Spanish police believe Abu Musab al-Zarqawi, a Jordanian terror suspect with links to Ansar al-Islam and Al Qaeda, was the brains behind the Madrid attacks.
Brisard told The Associated Press on Monday he believes Fakhet is the man referred to as "the Tunisian" in German police interrogation records of a terror suspect linked to Al Tawhid, a network run by al-Zarqawi in Germany.
Brisard said that during interrogation in 2002, alleged Al Tawhid member Shadi Abdellah said he was contacted by a man who identified himself as "the Tunisian" and said he wanted to incorporate Moroccans into Al Tawhid. Brisard said that man was Fakhet.
Brisard is working for lawyers for relatives of Sept. 11 victims and has a copy of a dossier prepared by Spanish Judge Baltasar Garzon, who is investigating an alleged Al Qaeda cell in Spain. Brisard also says he has access to terror-related files in Germany.
The investigation into the Madrid attacks has focused on the Moroccan Islamic Combatant Group, which has links to Al Qaeda and is related to a group suspected in deadly bombings last year in Casablanca, Morocco.
In France, authorities detained 13 suspected militants in a dawn raid Monday stemming from the attack in Casablanca, which killed 33 people and 12 bombers.
Those detained are suspected of belonging to the Moroccan Islamic Combatant Group, French prosecutor Yves Bot said. However, he said authorities do not have evidence linking them to the Madrid bombings.