A man has been arrested and charged with plotting to damage or destroy the Pentagon and US Capitol by using remote-controlled aircraft filled with plastic explosives.
Rezwan Ferdaus, 26, a US citizen, was also charged with attempting to provide support and resources to al Qaeda in order to carry out attacks on US soldiers stationed overseas, U.S. attorney's office in Boston said.
He was caught in an undercover operation.
"The conduct alleged today shows that Mr Ferdaus had long planned to commit violent acts against our country," US Attorney Carmen Ortiz said in a statement.
The public was never in danger from the explosive devices, which were controlled by undercover FBI employees, she said.
Authorities allege that Mr Ferdaus, a physics graduate from Northeastern University in Boston, began planning to commit a violent "jihad" against the United States in early 2010.
Mr Ferdaus, of Ashland, Massachusetts, about 40kms west of Boston, is alleged to have modified mobile phones to act as electrical switches for an improvised explosive devices (IEDs).
He supplied the phones to the undercover FBI agents, who he believed were members of, or recruiters for, al Qaeda.
"During a June 2011 meeting, he appeared gratified when told his first phone detonation device had killed three US soldiers and injured four or five others in Iraq.
Mr Ferdaus responded, "That was exactly what I wanted," the federal affidavit said.
He told agents he planned to attack the Pentagon using "small drone airplanes" filled with explosives and guided by GPS equipment. He later expanded that plan to include an attack on the US Capitol.
"In May and June 2011, Mr Ferdaus delivered two thumb drives to the UCs (undercover agents), which contained detailed attack plans with step-by-step instructions as to how he planned to attack the Pentagon and Capitol," authorities said.
He travelled to Washington to conduct surveillance and take photographs of his target, and identified sites at East Potomac Park, near the Capitol, from which he planned to launch his explosive-filled aircraft.
Mr Ferdaus' arrest came immediately after he took possession of various weaponry from the undercover agents - including explosives, grenades and AK-47 assault rifles - and brought them to and locked them in his storage unit.
