Bombers prepared to inflict more shock and harm to grab attention

The scale of its carnage in Madrid and the indiscriminate way in which innocent commuters were targeted may mark an alarming new trend in terrorism after 11 September 2001, experts said.

The scale of its carnage in Madrid and the indiscriminate way in which innocent commuters were targeted may mark an alarming new trend in terrorism after 11 September 2001, experts said.

Despite the huge resources devoted to fighting the "war on terror", bombers are still getting through and causing enormous loss of life by hitting soft targets. "Terrorists are becoming more indiscriminate and they are having a wider impact on communities," said Tim Dunne, a Canadian military analyst and author of a study on terrorism.

"It looks as if terrorists are becoming more ambitious in their aims. They want to do more damage, inflict more harm and cause more shock - to grab the attention of their public and force governments to react."

One diplomat who has specialised in terror issues said: "September 11 has set the bar for mass killings and for the shock that could come from them. What we have been worried about is that 9/11 would start a new type of attack: how much horror can you get out of targeting large numbers?"

Manuel Coma, a security expert at Spain's Royal Elcano Institute, said al-Qa'ida had prompted an escalation of terror acts. "Since September 11, there has been a qualitative leap. Small attacks are no longer adequate. They have to aim higher to have influence," he said.

Experts are wary of drawing too many conclusions before it is clear whether the bombings were carried out by Eta, the militant Basque separatist group, or by groups with a Middle Eastern link.

Kevin O'Brien, a policy analyst with Rand Europe, a research organisation, said: "If indeed it is Eta then this is a massive escalation in terms of the type of attack and the type of casualties. The largest number killed by Eta in one attempt was 21 people in 1987; this is the single biggest terrorist attack in Europe since Lockerbie.

"This would represent a great breach of practice if it were committed by a nationally based [European] terror group. If it turns out to be jihadist, that is exactly the type of attack which they have mounted in the past."

The bombings departed from traditional Eta tactics by giving no prior warning and by making use of multiple, simultaneous explosions, a favoured tactic of al-Qa'ida. Even if Basque separatists are linked, there remains a possibility that a splinter group was responsible, or that more died than was expected.

What is clear is that recent security crackdowns may have created their own dynamic, prompting terrorists to choose more prosaic targets but aim for a greater number of casualties.