Washington has heightened its aviation security since January for travelers coming into the United States after Umar Farouk Abdulmutallab tried to detonate explosives hidden in his underwear on a flight to Detroit from Amsterdam.
"I believe that (the new measures) would in all likelihood have gotten Abdulmutallab before he got on board his flight to Detroit," Secretary Janet Napolitano told Reuters in Nigeria's capital Abuja.
Napolitano was in Africa's most populous country to meet with her African counterparts ahead of a regional summit on bolstering global aviation security.
The new security measures replaced the mandatory screening of air travelers from 14 mostly Muslim countries that had angered some allies, including Nigeria, when it was imposed.
"(The measures) are not based on national origin, gender or anything else. It is based on particular passengers that is passed on before they board the plane," she said.
Nigeria said its inclusion on the US list, which included Cuba, Iran and Iraq, could have threatened bilateral ties.
The new system announced on April 2 would require US-bound travelers who match information about terrorism suspects, such as a physical description, partial name or travel pattern, to undergo additional screening.
"Aviation security begins before a passenger even gets to an airport," the 52-year-old former Arizona governor said.
"In other words, we are pushing the perimeter out. It is about information collection, it is about information sharing and passenger vetting so you know which passengers may be problematic." Under this new system, Abdulmutallab would likely have received a second screening before boarding his flight in Amsterdam since he was in a database of about 550,000 people with suspected terrorist links.
The United States is by far Nigeria's largest trade partner, accounting for nearly 45 percent of the OPEC member's exports, mainly crude oil, according to the IMF.
Napolitano, who is the first woman to head the sprawling Homeland Security Department, is one of a few people being mentioned as a possible replacement to retiring Supreme Court Justice John Paul Stevens, according to legal experts.
"Look, I am focused on the job. It is a big job that I have as Secretary of Homeland Security," she said. "I need this speculation doused." An administration official said on Friday that US President Barack Obama is considering "about 10" people as potential nominees.
