SECURITY: The Basque terrorist group Eta last night denied responsibility for train bombings that killed at least 199 people, Basque media reported, citing phone calls from the separatist organisation.
Spanish authorities at first blamed Eta outright for the attacks and have since called the outlawed group the prime suspect while not ruling out Islamic extremists.
And adding credence to the belief that an Islamic group rather than Eta may have been behind the atrocity, a radio station reported that the backpack bombs were set off by mobile phone and contained copper detonators, which are not generally used by Eta. The report, on private radio station Cadena Ser, quoted security sources as saying the components may point to the bomb having been set by an extremist Islamic group such as al-Qaeda.
The report said the bombs were activated by mobile telephones which had had their alarms set for 7:39 a.m. on Thursday.
The detonator in an unexploded bomb recovered by police contained a copper detonator whereas the detonators commonly used by Eta are made of aluminium, the report said.
On Thursday, the initial belief that Eta was behind the bombs was challenged when a van was found at a station believed used by the bombers. It contained a tape of verses from the Koran and detonators. Later, a London-based newspaper, al-Qusa al-Arabi, reported an admission of responsibility by a group linked to Osama bin Laden.
Yesterday's Eta denial was relayed by a presenter for ETB Basque public television who said that "an Eta message has arrived saying that it bore no responsibility for the attack".
The Basque newspaper Gara also said on its website that it had received a phone call from a person claiming to represent Eta saying it "had no responsibility whatsoever" for the attacks which involved 10 bombs set off simultaneously on four trains on Thursday morning.
There was no way to independently confirm the authenticity of the call, but Eta has claimed responsibility for past attacks through ETB and Gara.
ETB said the caller identified himself as one of two masked Eta leaders who last month delivered a videotaped message declaring a partial truce limited to the Catalonia region in northwest Spain.
There has been speculation that the manner of the bombings and the scale of the attack indicated possible involvement by Islamist militants, though Madrid insists Eta is the most likely suspect. Some security analysts have also suggested a militant splinter group of Eta was behind the attacks.
Interior ministry officials were unavailable to comment.
Political leaders in the Basque region were cautious about reading too much into the purported Eta messages.
"This is a day of demonstration, of repulsion and condemnation ... over the massacre of yesterday," Mr Patxi Lopez, leader of the Socialist party in the Basque country, told reporters at the march in the largest Basque city of Bilbao.
"But it is no less true that we need to know the truth (about what happened)," Mr Lopez said. "I always believe the Interior Ministry more than Eta."
The backpack examined by investigators was picked up from one of the mangled trains and put together with other lost luggage after the blasts, Cadena Ser said.
It was later found to contain an unexploded bomb, which police defused, according to the report.
The backpack contained 10.2 kg (22 lbs) of Spanish-made plastic explosives. The detonator was also Spanish-made.
The backpack also contained about one kilo of screws and nails. These are sometimes used as shrapnel to increase the destructive power of a bomb.
"Police are analysing the kind of explosive found in this backpack," an Interior Ministry source said. He said he could not yet say whether the bomb components were of a type commonly used by Eta.
Ten bombs exploded on packed commuter trains entering Madrid on Thursday during the busy morning rush hour in the worst guerrilla attack in Spain's history. Four others did not go off.