March 12 (Bloomberg) -- Spain is investigating the al-Qaeda and ETA terrorist networks for the groups' involvement in the bombings on rush-hour trains that killed 198 people yesterday in Madrid, Spanish Prime Minister Jose Maria Aznar said.

``No line of investigation will be ruled out,'' Aznar said at a press conference when questioned about the two terrorist organizations. ``If we were certain'' of the authorship ``we would be telling you.'' He didn't mention ETA or al-Qaeda by name.

A letter purportedly from al-Qaeda said the terrorist network carried out the attacks on commuter trains and warned the group will attack the U.S. Spain's government has said its main suspect is ETA, which has killed more than 800 people in 35 years to force the government to grant independence to Basques.

``Our central thesis is that it was ETA, which already tried to carry out just such a massacre three times,'' said Rodrigo Rato, Spain's first deputy prime minister and economy minister. ``That's the principal line of investigation, though we're not ruling out any others.''

Results from investigations by Spanish security personnel will be revealed ``soon,'' Aznar said. He promised to reveal ``absolutely every'' detail of the findings to the public.

Interior Minister Angel Acebes said the bombs contained dynamite similar to that used by ETA. The attack was the worst terror assault in Spain's modern history.

March 11

``March 11 now has its place in the history of infamy,'' Aznar said in a television address yesterday. ``Terrorists tried to cause as much pain as possible.''

The letter was sent to Al-Quds Al-Arabi, an Arabic daily newspaper in London, which faxed it to Bloomberg News. The statement says an attack on the U.S. is almost ready and names the U.K., Japan and Italy as possible targets. It hasn't been verified as an al-Qaeda message.

The coordinated attack, involving 10 bombs targeting passenger trains, is the worst terrorist incident in Spanish history. More than 1,460 people were injured. It came before Sunday's general election in Spain. Aznar called on Spaniards to hold nationwide demonstrations later today to protest the attack. The country started three days of mourning today.

Spanish security authorities ``will produce results soon, so that we can know all the details and responsibilities that exist behind these criminal attacks,'' Prime Minister Aznar said.

Aznar said he would earmark 140 million euros in aid for bomb victims, which include nationals from almost one dozen other countries.

Foreign Leaders

The prime ministers of France and Italy, Jean-Pierre Raffarin and Silvio Berlusconi, plan to travel to Madrid to join the demonstrations, Aznar said. Deputy U.K. Prime Minister John Prescott will also attend, Sky News reported.

Spain's Cadena Ser radio said a suicide bomber may have struck one of the trains, citing three unidentified members of the anti-terrorist police force. No suicide bombers were involved, government spokesman Eduardo Zaplana said late yesterday on national television.

Health authorities this morning raised the death toll to 198. Eighty bodies remain unidentified.

The French government today raised France's terrorism alert by one level. The Basque country, which ETA wants to separate from Spain, straddles the Franco-Spanish border and reaches into southwest France.

Stocks Down

U.S. and European stocks fell and the dollar dropped against the euro after the bombings. The Standard & Poor's 500 Index in the U.S. yesterday fell 1.5 percent and Europe's Dow Jones Stoxx 50 Index slid 2.8 percent, led by travel-related companies.

Al-Quds editor Abdel Bari Atwan said on Sky News that the letter his newspaper received ``uses similar language and the same style of al-Qaeda.'' The statement ``could be authentic,'' he said.

The letter says: ``We're letting Muslims around the world know about an attack against America now in its final stages 90 percent, God willing, soon.'' Japan, the U.K. and Italy haven't taken heed of warning messages sent in the past, it said. The message is signed by ``the fighters of Abi Hafez Al Masri (Al- Qaeda)'' and dated March 11.

Spanish investigators found a stolen van with seven detonators and an Arabic tape with content from the Koran in Alcala de Henares, about 20 miles from Madrid. The authorities said the van may be linked to the attacks.

``All lines of investigation are open,'' said Acebes, the interior minister. The tape in the van included no threats and is of a kind typically used to teach the Koran, the Muslim holy book, he said.

Batasuna

Aznar, while condemning the attacks, didn't directly name ETA. Mariano Rajoy, picked by Aznar to lead the Popular Party in Sunday's election, said he had ``no doubt'' ETA was behind the attacks.

Arnaldo Otegi, leader of the banned Basque separatist party Batasuna, which Spanish courts link to ETA, said the group probably wasn't behind the attacks. Otegi said the attack could have been the work of the ``Arab resistance.''

ETA, whose initials stand for Euskadi ta Askatasuna, or Basque Homeland and Freedom, began a campaign for an independent state in Basque-speaking areas of northern Spain and southwestern France in the late 1960s.

The mystery of who was behind yesterday's blasts deepened because ETA didn't alert anyone in advance about the bombs, Spanish officials said. The terrorist group typically informs the media of imminent attacks.

Worst Attack

ETA's worst attack in terms of lives lost was the 1987 bombing of a shopping center in Barcelona that killed 21 people. Two weeks ago, police arrested suspected ETA members in a truck with explosives headed for Madrid.

Mass demonstrations typically follow ETA attacks. The biggest was in 1997 when millions of people demonstrated nationwide to call for an end to violence after ETA kidnapped and threatened to kill Miguel Angel Blanco, a Popular Party council member of Ermua in the Basque region. ETA subsequently carried out the threat and killed the official.

Police warned of violence before Sunday's elections that pit the Popular Party, which has ruled Spain for eight years, against the opposition Socialists. Both parties, which have vowed to crush ETA, suspended election campaigning yesterday.

The attack is the deadliest in Spain since ETA was founded in 1959 during the dictatorship of General Francisco Franco. The regime banned the Basque language, suppressed its culture and jailed its leaders.

To contact the reporters on this story: Todd White in Madrid at at twhite2@bloomberg.net; Paul Tobin in Madrid at ptobin@bloomberg.net

Last Updated: March 12, 2004 06:57 EST