The head of Al Qaeda's military faction in Yemen  posted an audio message online on Sunday warning Americans that they are vulnerable to attacks.
Qassim Al Rimi spoke of how the recent Boston bombings had revealed the remaining fragility of the American security system, as he called on Muslims to defend their religion.
Rimi is head of Al Qaeda in the Arabian Peninsula (AQAP) , widely regarded to be the most militant and active branch of the unquantifiable terrorist group.
He spoke directly to Muslims, telling them that bombs such as those used by the Chechen brothers in the Boston attacks are easily made and within "everyone's reach".
“The Boston events... and the poisoned letters (sent to the White House), regardless of who is behind them, show that your security is no longer under control, and that attacks on you have taken off and cannot be stopped,” he said, in the message entitled: “A letter to the American people," he said, as reported by AFP.
“Every day you will be hit by the unexpected and your leaders will not be able to defend you".
He spoke of the killing of Al Qaeda founder Osama bin Laden  and top US-Yemeni cleric Anwar Al Awlaki, who was killed by a US drone in 2011 , saying that despite these deaths being considered victories by America, it had not deterred the group from its mission.
“Have you eliminated the jihadist groups that have spread everywhere after they had only been in Afghanistan? Today, they are in your land or close to it,” he said in the recording.
Awlaki proved a influential figure in AQAP due to his fluent English and oratory skills, which enabled him to record a huge number of wildy popular YouTube videos and podcasts which proved an incredibly effective recruitment tool for the group. Awlaki published a 'Message to the American People', in which he called on them to revolt against their infidel neighbours and defend Islam in light of the US' "colonialst" foreign policies.
Espousing Awlaki, Rimi spoke directly to Muslims living in America and called on them to be "steadfast in your religion" and to continue with terrorist acts, such as those witnessed in Boston.
“Carry out your obligations, defend your religion and follow in the footsteps of those who supported their religion and Ummah (Muslim nation) while they are in their enemy's den,” he said, according to AFP.
Tamerlan died during a shootout with police. His brother is still in custody after an extensive manhunt was launched around the eastern American city to find the fugitives.