WASHINGTON — The CIA thwarted an ambitious plot by al-Qaida’s affiliate in Yemen to destroy a U.S.-bound airliner using a bomb with a sophisticated new design around the one-year anniversary of the killing of Osama bin Laden, U.S. officials said 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-Qaida developed a more refined detonation system, U.S. 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.

Sen. Dianne Feinstein, D-Calif., who heads the Senate Intelligence Committee, told reporters Monday that she had been briefed about an “undetectable” device that was “going to be on a U.S.-bound airliner.”

There were no immediate plans to change security procedures at U.S. airports.

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

White House spokeswoman Caitlin Hayden said President Barack Obama learned about the plot in April and was assured the device posed no threat to the public.

“The president thanks all intelligence and counterterrorism professionals involved for their outstanding work and for serving with the extraordinary skill and commitment that their enormous responsibilities demand,” Hayden said.

The operation unfolded even as the White House and Department of Homeland Security assured the American public that they knew of no al-Qaida plots against the U.S. around the anniversary of bin Laden’s death. The operation was carried out over the past few weeks, officials said.

“We have no credible information that terrorist organizations, including al-Qaida, are plotting attacks in the U.S. to coincide with the anniversary of bin Laden’s death,” White House press secretary Jay Carney said on April 26.

On May 1, the Department of Homeland Security said, “We have no indication of any specific, credible threats or plots against the U.S. tied to the one-year anniversary of bin Laden’s death.”

The White House did not explain those statements Monday.

The CIA mission was such a secret, even top lawmakers were not told about it as the operation unfolded, one U.S. official said Monday.

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.

The FBI and Department of Homeland Security acknowledged the existence of the bomb late Monday, but there were no immediate plans to adjust security procedures at airports. Other officials, who were briefed on the operation, insisted on anonymity to discuss details of the plot, many of which the U.S. has not officially acknowledged.

“The device never presented a threat to public safety, and the U.S. government is working closely with international partners to address associated concerns with the device,” the FBI said in a statement.

It’s not clear who built the bomb, but, because of its sophistication and its similarity to the Christmas bomb, counterterrorism officials suspected it was the work of master bomb maker Ibrahim Hassan al-Asiri or one of his protigies. Al-Asiri constructed the first underwear bomb and two others that al-Qaida built into printer cartridges and shipped to the U.S. on cargo planes in 2010.

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

The operation is an intelligence victory for the United States and a reminder of al-Qaida’s ambitions, despite the death of bin Laden and other senior leaders. Because of instability in the Yemeni government, the terrorist group’s branch there has gained territory and strength. It has set up terrorist camps and, in some areas, even operates as a de facto government.

But along with the gains there also have been losses. The group has suffered significant setbacks as the CIA and the U.S. military focus more on Yemen. On Sunday, Fahd al-Quso, a senior al-Qaida leader, was hit by a missile as he stepped out of his vehicle along with another operative in the southern Shabwa province of Yemen.

Al-Quso, 37, was on the FBI’s most wanted list, with a $5 million reward for information leading to his capture. He was indicted in the U.S. for his role in the 2000 bombing of the USS Cole in the harbor of Aden, Yemen, in which 17 American sailors were killed and 39 injured.

Al-Quso was believed to have replaced Anwar al-Awlaki as the group’s head of external operations. Al-Awlaki was killed in a U.S. airstrike last year.