A Northwest Airlines passenger from Nigeria, who said he was acting on al-Qaida's instructions, tried to blow up the plane Friday as it was landing in Detroit, law enforcement and national security officials said.
Passengers subdued the man and may have prevented him from detonating the explosives, the officials said.
"We believe this was an attempted act of terrorism," a White House official said.
Federal officials imposed stricter screening measures after the incident.
Rep. Peter King, R-N.Y., ranking GOP member of the House Homeland Security Committee, identified the suspect as Abdul Mudallad, a Nigerian. King said the flight began in Nigeria and went through Amsterdam en route to Detroit. There were 278 passengers aboard the Airbus 330.
There was nothing out of the ordinary until the flight was on final approach to Detroit, said Federal Aviation Administration spokeswoman Elizabeth Isham Cory. That is when the pilot declared an emergency and landed without incident shortly thereafter, Cory said in an e-mail message. The plane landed at 11:51 a.m. EST.
One of the U.S. intelligence officials said the explosive device was a mix of powder and liquid. It failed when the passenger tried to detonate it.
The passenger was being questioned Friday evening. An intelligence source said the Nigerian passenger was being held and treated in an Ann Arbor, Mich., hospital.
All the sources spoke on condition of anonymity because the investigation was continuing.
One law enforcement source said the man claimed to have been instructed by al-Qaida to detonate the plane over U.S. soil.
The official said an official determination of a terrorist act would have to come from the attorney general.
The official added that additional security measures are being taken without raising the airline threat level.
The official declined to describe what additional measures law enforcement was taking.
The White House was coordinating briefings for the president through the Homeland Security Department, the Transportation Security Administration and the FBI.
A law enforcement source said the explosives may have been strapped to the man's body but investigators weren't immediately certain, partly because of the struggle with other passengers.
One passenger from the flight was taken to the University of Michigan Medical Center in Ann Arbor, hospital spokeswoman Tracy Justice said. She didn't know the person's condition, or whether the person was a man or woman. She referred all inquiries to the FBI.
Passenger Syed Jafri, a U.S. citizen who had flown from the United Arab Emirates, said the incident occurred during the plane's descent. Jafri said he was seated three rows behind the passenger and said he saw a glow, and noticed a smoke smell. Then, he said, "a young man behind me jumped on him."
"Next thing you know, there was a lot of panic," he said.
Rich Griffith, a passenger from Pontiac, said he was seated too far in the back to see what had happened. But he said he didn't mind being detained on the plane for several hours. "It's frustrating if you don't want to keep your country safe," he said. "We can't have what's going on everywhere else happening here."
President Barack Obama was notified of the incident and discussed it with security officials, the White House said. It said he is monitoring the situation and receiving regular updates from his vacation spot in Hawaii.
J.P. Karas, 55, of Wyandotte, Mich., said he was driving down a road near the airport and saw a Delta jet at the end of the runway, surrounded by police cars, an ambulance, a bus and some TV trucks.
"I don't ever recall seeing a plane on that runway ever before and I pass by there frequently," he said.
Karas said it was difficult to tell what was going on, but it looked like the front wheel was off the runway.
"We encourage those with future travel plans to stay in touch with their airline and to visit http://www.tsa.gov for updates," Homeland Security Department said in a statement.
Homeland Security Secretary Janet Napolitano has been briefed on the incident and is closely monitoring the situation.
The department encouraged travelers to be observant and aware of their surroundings and report any suspicious behavior to law enforcement officials.
Jakes reported from Baghdad, Iraq. Randi Berris and Jim Irwin in West Bloomfield, Mich., and Devlin Barrett, Shelley Adler and Joan Lowy in Washington, and Philip Elliott in Oahu, Hawaii, contributed to this report.