A statement posted on Friday on an Islamic Website in the name of an Al Qaeda-linked group claimed responsibility for the July 21 blasts targeting London's transport system.
The group, Abu Hafs al Masri Brigade, also claimed responsibility for the July 7 bombings, which killed 56 people and four suicide bombers.
The statement's authenticity could not be immediately verified and there has been doubt cast over the veracity of the group's past claims.
"Our strikes in the depths of the capital of the British infidels are only a message to other European governments that we will not relent and sit idle before the infidel soldiers will leave the land of the two rivers," said the statement.
The 'two rivers' in the statement refer to Iraq's Euphrates and Tigris rivers.
On Tuesday, another statement was issued in the name of the same group threatening to launch 'a bloody war' on the capitals of European countries that do not remove their troops from Iraq within a month.
"While we bless these strikes, our next attacks will be hellish for the enemies of God," said the latest statement.
"We will srike in the hearts of European capitals, in Rome, in Amsterdam and in Denmark where their soldiers are in still in Iraq pursuing their British and American masters," the statement added.
The Abu Hafs al Masri brigades are named after the alias given to Mohammed Atef, Osama bin Laden's top deputy who was killed in a United States airstrike in Afghanistan in November 2001.