WASHINGTON: The CIA thwarted an ambitious plot by Al Qaeda's affiliate in Yemen to destroy a US-bound airliner using a bomb with a sophisticated new design around the one-year anniversary of the killing of Osama bin Laden, Associated Press reported late Monday.

The plot involved an upgrade of the underwear bomb that failed to detonate aboard a jetliner over Detroit on Christmas 2009. This new bomb was also designed to be used in a passenger's underwear, but this time Al-Qaeda developed a more refined detonation system, US officials said.

The FBI is examining the latest bomb to see whether it could have passed through airport security and brought down an airplane, officials said. They said the device did not contain metal, meaning it probably could have passed through an airport metal detector. But it was not clear whether new body scanners used in many airports would have detected it.

The would-be suicide bomber, based in Yemen, had not yet picked a target or bought his plane tickets when the CIA stepped in and seized the bomb, officials said. It's not immediately clear what happened to the alleged bomber.

The operation unfolded even as the White House and Department of Homeland Security assured the American public that they knew of no Al Qaeda plots against the US around the anniversary of bin Laden's death. The AP learned about the thwarted plot last week but agreed to White House and CIA requests not to publish it immediately because the sensitive intelligence operation was still under way. Once officials said those concerns were allayed, the AP decided to disclose the plot Monday despite requests from the Obama administration to wait for an official announcement Tuesday.

US officials, who were briefed on the operation, insisted on anonymity to discuss the case, which the US has never officially acknowledged.

It's not clear who built the bomb, but, because of its sophistication and its similarity to the Christmas bomb, authorities suspected it was the work of master bomb maker Ibrahim Hassan al-Asiri. Al-Asiri constructed the first underwear bomb and two others that Al Qaeda built into printer cartridges and shipped to the US on cargo planes in 2010

Both of those bombs used a powerful industrial explosive. Both were nearly successful.