Washington (AFP) - The United States is on edge after the Paris terror attacks, tightening security amid fears of attacks by both "lone wolf" attackers and small cells guided from afar.
On Wednesday the FBI announced the arrest of a young American man in Ohio who is accused of planning an attack on the Capitol in Washington, the seat of Congress.
An undercover officer recorded him in conversations held both face-to-face and over the Internet, advocating violent attacks in conversations held both face-to-face and over the Internet.
The same day an American jihadist was sentenced to 20 years in prison in Florida for trying to support al-Qaeda.
Meanwhile, new charges were filed against the Qazi brothers, Americans arrested in 2012 for trying to detonate a bomb in New York.
FBI director James Comey spoke recently of the spread of the terrorist threat since the September 11, 2001 attacks.
Experts see a rising number of "lone wolves" and small jihadist cells of the kind formed by the Kouachi brothers in France and Amedy Coulibaly, who staged the recent attacks in France.
These are Western-born Muslims inspired by the ideology and tactics of al-Qaeda or the Islamic State group, who decide to stage an attack with or without the direct support of the organization.
The threat is almost undetectable and extremely hard to prevent, said analyst Max Abrahms, who expects the FBI to break up more of the kind of operations envisaged by the Ohio suspect.
- Al-Qaeda in Yemen in spotlight -
The attack against the French newspaper Charlie Hebdo was claimed by al-Qaeda in the Arabian Peninsula, the Yemeni branch of the movement, which is "particularly worrisome for the US."
"AQAP is making a lot of noise right now and understandably that that gives US security officials jitters," said Abrahms, who teaches at Northeastern University.
"It makes perfect sense, particularly because the attack was linked to AQAP that the US would ramp up its own security," he added.
In the wake of the Paris attacks, which left 17 dead, US Secretary of Homeland Security Jeh Johnson ramped up security and surveillance around government buildings and at airports.
"It is time to be extra vigilant," he said, announcing efforts to raise awareness among religious and ethnic communities across the United States.
"The continuing terror threat" overshadowing the United States was hammered home with all US security services and police during a teleconference Wednesday with the FBI and Homeland Security.
"Continued vigilance, information sharing, and coordination at all levels are the key to effective prevention, and provided an inclusive forum to share relevant information with our law enforcement partners," said an FBI statement.
Two congressional probes will focus on homegrown terrorism.
The Republican chairman of the Homeland Security Commission of the House of Representatives, Michael McCaul, said it is a matter of determining how the US government fights these domestic threats and fixes the gaps in its in defense systems to protect the US.
Terrorists are determined to attack the United States and are trying to turn Americans into jihadists, he said.