WASHINGTON (AFP) - Al-Qaeda Wednesday claimed in Internet statements to have carried out a suicide attack on the Danish embassy in Islamabad which left at least six dead, SITE monitoring services said. Monday's attack was said to be in revenge for the publication in Danish newspapers of cartoons according to statements posted on Islamic militant forums, SITE said. "One of the heroes of 'Qaedat al-Jihad' carried out a suicide operation on the morning of Monday," said the statement signed by one of the terror network's leaders, Mustafa Abu al-Yazid. The attack was "in revenge against the state of infidelity, called 'Denmark', that posted cartoons hostile to the messenger of Allah," he added, according to an English translation provided by the SITE intelligence group. "This operation is a warning to the infidel state and those who ride with it, so that they are deterred from their sin... and so that they apologize for what they did," Yazid added. SITE, a US-based group which monitors Islamic militant Internet websites and chat rooms, said the message was posted Wednesday on several forums. Danish intelligence officials said earlier Wednesday that the attack had been meticulously planned for a "long time." "Preliminary information gleaned from the car used in this suicide attack seems to indicate that it had been planned for a long time with precision," said the PET intelligence service in a statement. Denmark's secret services have sent three experts to Islamabad as part of their investigation. One Danish citizen of Pakistani origin and two Pakistani employees were among the dead in the blast that badly damaged the embassy and the offices of a UN-backed aid agency. Al-Qaeda extremists called for attacks on Danish targets after Danish newspapers ran caricatures. Yazid said Al-Qaeda congratulated "the Pakistani mujahideen ... the pioneers of the religious fervour and Islamic zeal, who participated" in the attack. And he added the group would soon publish the will of the suicide bomber.