Hobbled by leg irons, a young Nigerian accused of trying to blow up a US plane on Christmas Day pleaded not guilty during his first court appearance amid heightened security.

Umar Farouk Abdulmutallab, 23, spoke softly from the dock Friday to confirm his name, how it was spelled and his age. His expression flat, his eyes averted from the gathered crowd, he said he understood the six charges against him.

His court-appointed lawyer, Miriam Siefer, entered the plea of not guilty to all six charges, including attempted murder of 290 people on board the plane and trying to use a weapon of mass destruction. He faces life imprisonment if convicted.

"At this time our client would like to enter a plea of not guilty," Siefer said, but added "we have -- with our client's consent -- consented to detention."

Abdulmutallab, son of a prominent Nigerian banker, was arrested after the botched Al-Qaeda plot, in which explosives allegedly stitched into his underwear failed to detonate aboard a Northwest flight from Amsterdam to Detroit.

He was badly burned when the device sparked a fire. Asked if he had taken any medication in the past 24 hours, he said "Yes. Painkillers," holding his left hip.

It was not US intelligence that thwarted the attack, but passengers and crew, who tackled and restrained Abdulmutallab before he was escorted off the plane.

The foiled bombing triggered global alarm, leading the United States to adopt stringent new screening and security measures at airports around the world. Dozens of names have also been added to no-fly lists.Related article: Obama orders 'immediate' steps after security failure

President Barack Obama on Thursday ordered a sweeping overhaul of flawed intelligence services, which he has blamed for missing red flags that could have detected the plot.

Probes revealed that US analysts knew Abdulmutallab was an extremist and that Al-Qaeda in the Arabian Peninsula was plotting an attack, but did not connect the dots.

Legal experts believe this case is going to take months to come to a conclusion. Related article: US 'plane bomber' met radical cleric

"There are so many agencies - with initials you know and initials you don't - involved in a case that transcends territorial boundaries," said attorney James Thomas, who represented one of four North African immigrants in a 2003 terror trial in Detroit.

He noted that evidence for this trial was being gathered in Yemen, Nigeria, the Netherlands and elsewhere, and it will take months to digest, declassify and share it with the defense team.

Ahead of the arraignment, US marshals helped local police secure the area around the ornate, marble-floored Theodore Levin Courthouse.

Metal barricades blocked off the street along the austere building. Inside, two bomb-sniffing dogs and their handlers had earlier checked every room and, as is now standard for US courtrooms, every visitor to the Depression-era courthouse passed through a metal detector.

A man who said he represented the Nigerian embassy but would not give his name told reporters that Abdulmutallab's family had not attended the hearing.

Citing British intelligence officials, CBS television reported the former University College London student boasted during his interrogation that some 20 others were being trained to carry out similar attacks.

US officials have said Abdulmutallab has provided useful leads during interrogations with FBI and other US agents who are leading the investigation.

The head of national intelligence meanwhile named former CIA director John McLaughlin to lead a probe into US intelligence failures exposed by the Christmas Day attack and a US soldier's November shooting rampage at a Texas army base.

Both Abdulmutallab and Major Nidal Hasan, the army psychiatrist who trained his guns on fellow servicemembers killing 12 soldiers and one civilian, are believed to be inspired by a radical US-born Islamic cleric now in Yemen -- Anwar al-Awlaqi.

In a continued sign of the heightened vigilance, the FBI arrested two alleged associates of an Afghan immigrant accused of planning bombings in New York around the anniversary of the September 11, 2001 attacks.

One of the men, taxi driver Zarein Ahmedzay, pleaded not guilty after a New York judged charged him with making false statements to the FBI.

In Detroit, around 20 demonstrators stood shivering outside the courthouse holding American flags and signs declaring "Not in the name of Islam" and "Islam is against terrorism."

"Muslims here to tell you: Go to hell," read a sign held by Majed Rizki, 48, of nearby Dearborn, Michigan.

"It was a sin against humanity, against civilization," Rizki said of the bombing attempt.

Majed Moughni, who moved to the Detroit area from Lebanon, said he was worried there would be a backlash against Muslims.

"We're trying to unite as Muslims and we're going to eradicate all terrorism from our homes and our mosques and we're going to send terrorists back to the caves of Afghanistan," he said.