Doubt over al Qaeda claim
Spanish bombing probe expands
Identifying bomb victims difficult task
(CNN) -- A group saying it speaks for al Qaeda has claimed responsibility for the Madrid train bombings in an e-mail to an Arabic-language newspaper in London.
However, intelligence officials have said the group does not speak for al Qaeda and has been unreliable in the past.
Spanish officials said they are investigating the possibility of Arabic terrorist involvement, but that the prime suspect behind Thursday's bombings is the Basque terror group ETA.
"The main line of investigation remains on ETA," Spanish Foreign Minister Ana Palacio told CNN. (Main story)
Khalid al-Shami, political editor of Al Quds Al Arabi in London, said their office received an e-mail letter from the Abu Hafs al-Masri Brigade on Thursday.
In the letter, the group called the Madrid bombings the "death train operation," and said it wasn't disturbed by the deaths of innocent people.
"We in Abu Hafs al-Masri aren't saddened by the fall of what you call civilians. Is it acceptable for them to kill our women, children, elderly and youth in Afghanistan, Iraq, Palestine, and Kashmir, but forbid us to kill them?" the letter said.
The missive also threatened another attack is coming soon.
"And we will alert all Muslims around the world that an attack from the Wind of Black Death is imminent. It is currently in the final stages, 90 percent complete, God willing soon. It will happen at the appropriate time for Mujahadeens and will make believers joyous," the letter said.
It is not the first time the paper has received letters from the group.
The group claimed responsibility for the attacks last year in the Turkish city of Istanbul on two synagogues, the British consulate and a British Bank.
Intelligence sources have consistently told CNN that the Abu Hafs al-Masri Brigade does not speak for al Qaeda, and there is question as to whether it exists at all beyond one person with a computer and a fax machine.
For example, this group claimed responsibility for the U.S. power blackout last summer, a claim that turned out not to be true.
Just last week it claimed al Qaeda was not behind a car bombing in Iraq, which many intelligence officials believe was the work of an al Qaeda-related group.
CNN consultant Paul Eedle in the past has suggested the Abu Hafs al-Masri Brigade may be more interested in waging a propaganda war than in truthfully revealing who is behind particular acts of terror.