WASHINGTON - Investigators piecing together an attempt to bring down a transatlantic airliner said yesterday that the suspect had concealed a small bag holding a deadly concoction on his body, an explosive that the right airport equipment would have easily detected.

The Nigerian passenger's success in smuggling the material aboard Northwest Flight 253 to Detroit and partially igniting it Friday prompted the Obama administration to promise a sweeping review of aviation security.

Adding to the air-travel jitters, a second Nigerian man was detained after he locked himself in a bathroom on yesterday's Flight 253. He was belligerent but genuinely sick, officials said, after the plane in an abundance of caution, had been routed to a remote location at the Detroit airport for screening before passengers were let off. Investigators concluded that the man posed no threat.

Despite the government's decision after Friday's attempted attack to mobilize more air marshals, none was on yesterday's Flight 253, which took off from Amsterdam, according to a government report.

Travelers returning home from the holidays yesterday described extensive searches before they were allowed to board flights from overseas and restrictions on their movements as the planes approached the United States.

Passengers flying into the United States should expect additional security precautions such as increased screening at gates, pat-downs, and bag searches, the Transportation Security Administration said last night.

White House spokesman Robert Gibbs announced a review of air safety on two broad fronts, saying the government will investigate its systems for placing suspicious travelers on watch lists and for detecting explosives before passengers board.

Both lines of defense were breached in an improbable series of Christmas Day events that spanned three continents and culminated in a fire and a struggle aboard the Northwest jet shortly before its safe landing in Detroit. Law enforcement officials said they believed the suspect had tried to ignite a two-part concoction of the high explosive PETN and possibly a glycol-based liquid explosive, setting off popping, smoke, and some fire but no detonation.

Umar Farouk Abdulmutallab, 23, an Islamic devotee once nicknamed "The Pope" as a sign of respect by classmates in London, was released from a Michigan hospital in custody of federal marshals yesterday after being treated for burns. He is charged with trying to destroy an aircraft and placing a destructive device in a plane.

His lawyer said yesterday that Abdulmutallab was in a federal prison in Milan, Mich.

Homeland Security Secretary Janet Napolitano hastened to assure people that flying is "very, very safe."

She said Abdulmutallab "was stopped before any damage could be done. I think the important thing to recognize here is that once this incident occurred, everything happened that should have."

That brought a sharp rebuke from Rep. Peter King of New York, the top Republican on the Homeland Security Committee. "It's not reassuring when the secretary of homeland security says the system worked," King said. "It failed in every respect."

Sen. Mitch McConnell of Kentucky, the Republican leader in the Senate, said, "It's amazing to me that an individual like this who was sending out so many signals could end up getting on a plane going to the U.S."

An apparent malfunction in a device designed to detonate the PETN may have been all that saved the 278 passengers and the crew.

No undercover air marshal was on board; passengers and crew subdued the suspect after he tried to set off the explosion. He succeeded only in starting a fire on himself.

Law enforcement officials said Abdulmutallab had hidden below his torso a condom or condomlike pouch containing PETN, the primary ingredient in detonating cords used for industrial explosions.

Airport "puffer" machines that blow air on a passenger to collect and analyze residues probably would have detected the powder, as would have bomb-sniffing dogs or a hands-on search using a swab, the officials said, but most passengers in airports go through only magnetometers, which detect metal rather than explosives.

Authorities said Abdulmutallab had told them after his arrest that his plan originated with al-Qaeda's network inside Yemen, a link the U.S. government has avoided making so far. Napolitano said there was no indication yet that Abdulmutallab was part of a larger terrorist plot, though possible ties to al-Qaeda are under investigation.

Abdulmutallab had been placed on a watch list with more than 500,000 names in November, but not one that prevented him from flying into the United States. He came to the attention of U.S. intelligence last month when his father, a Nigerian banker, told the U.S. Embassy in Nigeria that his son's views were becoming increasingly extreme.

Despite that red flag, Abdulmutallab was not elevated to more exclusive - and perhaps manageable - lists of about 18,000 people who are designated for additional security searches or barred from flying. Napolitano said that would have required "specific, credible, derogatory information" that authorities did not have.

A U.S. official said the father's concerns had been shared among those in the Embassy, including liaison personnel from other agencies based there, such as the FBI. The alert was then relayed to Washington and again shared among agencies.