Al-Qaida's affiliate in Yemen was not behind the Sept. 3 crash of a UPS cargo plane in Dubai and falsely took responsibility for the incident, according to the FBI and Department of Homeland Security.

Al-Qaida in the Arabian Peninsula's claim of involvement in the October mail bomb plot aimed at U.S.-bound planes was "credible," but the group took false credit for the earlier crash to bolster its image, according to an internal bulletin from the FBI and Department of Homeland Security.

The Associated Press obtained a copy of the bulletin.

"We assess that AQAP's assertion of responsibility for the 3 September 2010 crash of a UPS cargo plane in Dubai is false," the bulletin said in a message to other law enforcement agencies. "Other terrorist organizations have falsely claimed credit for events with a high media profile to bolster their image and external perceptions of their operational capabilities."

The Yemen-based terror faction had claimed responsibility last week for both the cargo plane crash and the recent mail bomb plot that was foiled when authorities found bombs wired inside computer printers seized in Dubai and Britain.

In its statement, al-Qaida's Yemeni offshoot said that it "downed the UPS airplane but because the enemy's media did not attribute the act to us, we kept silent about the operation until we could return the ball once more."

Authorities in the U.S. and the United Arab Emirates have found no evidence of an explosion aboard the UPS cargo plane. They have said the crash of the UPS plane shortly after takeoff was caused by an onboard fire.

Investigators have taken a second look at the incident in the wake of the parcel bomb plot, but found nothing so far to alter their earlier conclusion that the crash was an accident.

A security official in the UAE familiar with the investigations into the UPS cargo plane crash told The Associated Press that there was no change in the earlier findings and that the UPS crash in September was likely caused by fire.

A UPS spokesman, Norman Black, also said last week that his company had "no independent knowledge of this claim by al-Qaida," and noted that both UAE officials and U.S. National Transportation Safety Board officials had so far ruled out the possibility of a bomb.