The Moroccan immigrant accused of attempting a suicide attack against the US Capitol building waived his rights to preliminary and detention hearings before a court in Virginia.

Amine El Khalifi, 29, was arrested Friday in Washington near the Capitol building wearing what he thought was a bomb vest ready to be detonated.

Undercover FBI agents had given him the vest, which contained harmless material made to look like bombs.

He is charged with attempting to use a weapon of mass destruction against property of the United States. He faces the possibility of life in prison.

During a brief hearing in Alexandria, Virginia, Khalifi responded, "Yes," twice when the judge asked him if he understood the "serious nature of the charge" against him and if he renounced his rights to challenge his detention.

Judge John Anderson then said that "due to the serious nature of the charge and the immigration status... I require you to remain in custody."

Khalifi sported a beard and a green jumpsuit with the word "prisoner" marked on back during the hearing.

Khalifi is being defended by a court-appointed lawyer. Sources associated with the prosecutor said his case would be presented to a grand jury within 30 working days to decide formal charges against him.

He has lived illegally in the United States since 1999, when his tourist visa expired, according to federal court documents. He was living in an Alexandria apartment when he was arrested.

Khalifi had been under surveillance by the FBI since January 2011 after being reported to the authorities by a "confidential source."

The source reportedly said Khalifi had told other people at a meeting in Arlington, Virginia that "the group must prepare for war," according to a court document signed by an FBI agent.

An undercover FBI agent who introduced himself to Khalifi as "Yusuf," a member of an extremist militant group, convinced the Moroccan man he would assist him in an attack against US targets.

Yusuf gave Khalifi the defused bomb vest and a non-working MAC-10 automatic pistol he carried when he was arrested, according to the court documents.

Khalifi reportedly told the undercover FBI agent that he had a "desire to conduct an operation in which he would use a gun and kill people face to face."

Initially, he said he "would be happy to kill 30 people" in an attack he wanted to direct at US military installations, a synagogue or a restaurant frequented by military officials.

After he decided the Capitol would be his target, Khalifi spent nearly a month scoping out the building, venturing inside several times to conduct surveillance and asking the undercover FBI agent to remotely detonate the bomb if he encountered problems with security officers.