Umar Farouk Abdulmutallab, the Nigerian man charged with attempting to blow up a Christmas Day flight over Detroit, told investigators that about 20 other Muslims were being trained in Yemen for similar attacks, US broadcaster CBS said, citing the British intelligence services.
The attack on the Delta/Northwest Airlines flight was prevented only because the PETN explosive that Abdulmutallab smuggled on board failed to detonate.
An initial inquiry commissioned by US President Barack Obama found that the attack had been plotted by the Yemen affiliate of the terrorist group Al-Qaeda.
US flight security officials have tightened checks on people boarding US-bound flights. Passengers from 14 countries are being specially scrutinized, including from various Arabic-speaking countries and Nigeria.
According to CBS, the US has sent FBI agents to Ghana, where Abdulmutallab started his journey to the US after spending five months in Yemen.
US investigators believe that the suspected terrorist met an Al-Qaeda member in the Ghanaian capital, Accra, where he possibly received the PETN material which he then hid in his underpants, CBS reported.
The 23-year-old Nigerian, who is charged with trying to blow up the plane with 290 people on board, was arraigned in Detroit in federal court on Friday, where he pleaded "not guilty." He was indicted by a grand jury on six charges.
Eyewitnesses said the young man's legs were in chains in the court appearance. Wearing a white T-shirt and khaki trousers, Abdulmutallab sat with hanging shoulders, looking at the floor, giving a defeated impression, according to news reports. He spoke so softly that the judge had to ask him to to speak more loudly.
That image contradicted one given by a spokesman for the court, Rod Hansen, who said Abdulmutallab was calm and showed no emotions as he spelled his name and recited details of his schooling. The terrorist suspect was under the influence of pain killers related to his injuries when the explosive caught fire.
A quick-thinking passenger on the plane raced to the seat when flames appeared, wrestled the explosive from Abdulmutallab and put out the fire with the help of cabin crew.
Abdulmutallab had ignited the explosive as the plane was making its approach to the airport.
He faces life in prison. It could take months until the trial begins, but experts expect a relatively short process since he was caught in the act of trying to blow up the plane, with a plane full of witnesses.
His lawyers did not contest his being held in prison until a trial.