Al-Qaeda in the Arabian Peninsula (AQAP) has said it sent two parcel bombs on planes bound for the US last week, in messages on jihadist websites.
The regional offshoot of Osama Bin Laden's militant network also said it was responsible for bringing down a UPS cargo plane in Dubai in September.
The Yemen-based group vowed to continue to target the US and its allies.
The explosive devices were made safe after being found on two aircraft which had landed in Dubai and the UK.
Sent by cargo from the Yemeni capital Sanaa on 29 October, they were intercepted after a tip-off from an AQAP member who handed himself in in Saudi Arabia, UK officials said.
The messages accused the Saudi authorities of thwarting the attack and of "collaboration with the Jews".
The packages, which contained the powerful explosive, PETN, concealed in printer toner cartridges, were addressed to synagogues in Chicago.
Security forces in Yemen are hunting for AQAP's suspected bomb maker, Ibrahim al-Asiri, in connection with the plot.
On 3 September, a UPS cargo plane came down near Dubai airport shortly after take-off, killing two crew members.
Investigators have not yet determined what caused the crash. However, the UAE's civil aviation authority recently said there was no "presence of acoustic evidence or any forensic signature supporting the detonation of an explosive device".
The statement issued by AQAP said: "We downed the plane belonging to the American UPS company, but because the media of the enemy did not attribute responsibility for this work to us we kept quiet about the operation until the time came that we hit again."
"We wonder: Why did the enemy not show what happened to the UPS plane that was downed?" it asked.
"We say to [US President Barack] Obama: 'We struck three blows to your aircraft within one year. Allah willing, we will continue to strike blows against American interests and the interest of America's allies.'"