WASHINGTON -- The latest foiled bomb plot targeting an airliner is an indication that, while the device did not ultimately pose a threat, terrorists remain determined, U.S. Secretary of State Hilary Clinton said Tuesday.
"These terrorists keep trying ... to devise more perverse and terrible ways to kill innocent people, and it's a reminder as to why we have to remain vigilant at home and abroad in protecting our nation and in protecting friendly nations," she told reporters at a news conference in New Delhi.
On Monday, officials said U.S. and other intelligence agencies recently broke up the plot and had seized an explosive device that is similar to ones previously used by al Qaeda.
The plot was discovered before it threatened any Americans, and no airliners were at risk, one U.S. counterterrorism official said. A nonmetallic explosive device like the one used in the failed attempt to bomb a Detroit-bound jet in 2009 was recovered, the official said, adding that it was meant for use by a suicide bomber.
A spokesman for the Department of Homeland Security said authorities have "no specific, credible information regarding an active terrorist plot against the U.S. at this time," although they continue to monitor efforts to carry out such attacks.
U.S. President Barack Obama was told about the plot in April, and the attempt "underscores the necessity of remaining vigilant against terrorism here and abroad," the White House said.
The threat was foiled around the same time as the anniversary of the raid that killed Osama bin Laden, although a second U.S. counterterrorism official said the attempted attack was not timed to coincide with the death of the al Qaeda leader.
The FBI said it is conducting technical and forensic analysis on the improvised explosive device.
The device is similar to others previously used by al Qaeda in the Arabian Peninsula (AQAP), which Western officials describe as al Qaeda's most dangerous affiliate, the FBI said.
The device was meant to be put on a U.S.-bound airline, U.S. Rep. Peter King, chairman of the House Homeland Security Committee, told CNN's Anderson Cooper.
The New York Republican said discovery of the bomb plot is just one part of an ongoing operation.
"It's not over as far as the operation itself, which is why you're seeing very few details being given out," he said.
Both King and a senior administration official said the intended user of the bomb is no longer a threat.
The recovered device, which never made it near an airport or airplane, was not built to be a so-called body bomb, the official said.
"AQAP is the responsible group here," said a different senior U.S. official.
"While similar, a preliminary review of this device shows that it has some significant differences from the device used in the Christmas Day attack. It is clear that AQAP is revamping its bomb techniques to try to avoid the causes of the failure of the 2009 device," the official said, referring to the Detroit incident.
U.S. officials believe AQAP has more than 1,000 members in Yemen and connections to al Qaeda leadership in Pakistan.
Contacted Tuesday, Yemeni officials in the president's office, as well as in the Ministry of the Interior, said they had no information about the plot.
The Yemen affiliate of al Qaeda has been behind two of the most audacious attempts to target the United States in recent years: the attempted 2009 bombing and the printer bombs loaded onto cargo planes in 2010 and destined for an address in Chicago.
In both cases, U.S. authorities believe the bombs were built by Ibrahim al-Asiri. Both devices contained a main charge of PETN, a white powdery explosive that conventional "single beam" X-ray machines are rarely able to detect.
In 2009, al-Asiri fitted out his own brother, Abdullah al-Asiri, with a PETN-based underwear bomb to kill Prince Mohammed bin Nayef, a top Saudi security official. The device killed his brother instantly but failed to kill its target.
The government of Yemen has been fighting AQAP for years, with mixed results.
On Sunday, a senior AQAP operative wanted for his role in the USS Cole bombing was killed by an airstrike in Yemen, officials said.
Fahd al Quso, 37, was killed while riding in a vehicle in the Rafdh district in Shabwa province. He was hit by a CIA drone strike, U.S. officials told CNN.
In February, three months before he was taken out, al Quso was asked whether the group had stopped exporting terror operations to the outside.
"The war didn't end between us and our enemies," he replied. "Wait for what is coming."
The weekend attack plus the foiled airline plot delivered a "one-two punch" against AQAP, a senior administration official said.
"This was a key victory for us. It also reminds us, though, that this war is not going to end in Afghanistan," added King. "Al Qaeda has metastasized and morphed. And they are constantly attempting to find new ways to get at us."
CNN's Pam Benson,