The case against al-Qa'ida: Tightly co-ordinated attack bears hallmarks

Spain has previously been singled out as a target by al-Qa'ida operatives in retaliation for the Aznar government's support of US President George Bush in his "war on terror", which was declared after the attacks of 11 September 2001.

The hallmark of Osama bin Laden's organisation is the use of the suicide bomber, prepared to give his life in the war against symbols of Western power. Another characteristic of the Islamic fundamentalists is the lack of a claim. It took months before a video surfaced showing Bin Laden gloating about the success of the suicide hijackers who destroyed the World Trade Centre.

Usually, an al-Qai'da attack is followed by silence from the organisation, as was the case in the November 2003 bombing of the British consulate in Istanbul. On Thursday night, a letter, purporting to be from al-Qa'ida, claimed responsibility for the Madrid train bombings. The claim bore the signature "Abu Hafs al-Masri Brigades" and said they were "settling old accounts with Spain".

But last night the Spanish Interior Minister, Angel Acebes, cast doubt on the authenticity of the claim. He said: "I have talked today with the British Interior Minister [David Blunkett] and they call very much into question the credibility of that communiqué and we have to be very cautious about it. That organisation claims responsibility for all kinds of attacks every time there is a piece of news with a certain repercussion."

Jonathan Eyal, the director of the Royal United Services Institute, said the Israeli authorities were used to spurious claims from previously unknown organisations, which are "usually two men in an office with a fax machine".

Al-Qa'ida is known for the spectacular nature of its attacks, as illustrated by 11 September and the Bali nightclub bombing that killed 202 people in October 2002. The Bali bombing was triggered remotely from a mobile phone, a similarity that Spanish investigators have noted in the Madrid attacks.

Al-Qa'ida attacks are meticulously prepared with careful co-ordination and would include research about the timetables of the trains. After the bombings on Thursday, police found a van containing seven detonators and a tape in Arabic at a town near Madrid.

Spain was considered to be Europe's central planning station for the 11 September attacks. One of the suicide pilots, Mohammed Atta, spent a week in Spain prior to the attacks.

Some suspects detained in Spain after 11 September claimed under questioning that Spain's role was limited to recruitment, indoctrination and fundraising. They denied that Spain was a target for attack.

But Bin Laden, in a broadcast shortly after 11 September, referred to the former Islamic Kingdom of Al-Andalus, in what is now Spain, whose artistic scholarship was crushed by the crusading Catholic Christian monarchs Ferdinand and Isabella, who expelled all Muslims from Spain after 1492. There are therefore "old accounts" for Islamic fundamentalists to settle with Spain.

Mr Aznar's support for the war in Iraq pushed Spain into the frontline as a possible target. In the Casablanca bombings in May last year, when five co-ordinated attacks killed dozens across the city, one of the principal targets was a Spanish cultural centre. At the time, Spain conceded that its posture on the war in Iraq might have made it a target. Spanish soldiers and diplomats have been attacked in Iraq.

Although al-Qa'ida attacks have not always been thwarted, intelligence agencies have in the past picked up "chatter" which has enabled them to alert the public to the risk.