The group in its communiques praised recent lone-wolf style attacks against the West and calling for more of them.
"We urge you to strike America in its own home and beyond," says a letter attributed to Ibrahim al-Asiri.
Asiri, a citizen of Saudi Arabia suspected of being chief bomb-maker of al-Qaeda in the Arabian Peninsula.
The letter, according to a translation by SITE Intelligence Group, states, "America is first."
A U.S. counterterrorism official described the letter as "consistent with rhetoric the new leader stated upon taking over al Qaeda's most active affiliate that is known to threaten Western interests."
Asiri has a $5 million bounty on his head.
"The concern for Asiri would be that somehow the message would be traceable back to him -- whether by courier, or some digital stamp inside of the message," said Katherine Zimmerman of the American Enterprise Institute.
"We have seen US drone strikes kill a series of top al Qaeda leaders in Yemen over the past few months."
But if the letter is genuine, it would indicate that Asiri, who rarely makes public statements, is still alive.