A previously unknown group apparently linked to Al-Qaeda claimed responsibility for the London blasts on an Islamic website and said that "Britain is burning with fear".
The claim, which could not be verified, was made on the al-Qal'ah ( Fortress) internet site, and posted by the "Secret Organisation Group of Al-Qaeda of Jihad Organisation in Europe", and was picked up by BBC Monitoring.
The message said: "The heroic mujahidin have carried out a blessed raid in London. Britain is now burning with fear, terror and panic in its northern, southern, eastern and western quarters."
The statement claimed that the strikes were revenge for British military "massacres" in Iraq and Afghanistan. It appeared to warn Denmark and Italy that they would also suffer attacks if they did not withdraw troops from Iraq.
It went on: "O nation of Islam and nation of Arabism: Rejoice for it is time to take revenge from the British Zionist Crusader Government in retaliation for the massacres Britain is committing in Iraq and Afghanistan."
A spokesman for the Centre for the Study of Terrorism and Political Violence said the group was not known.