Osama bin Laden's son-in-law has been captured and is due to appear in court in New York on Friday on charges he plotted with the Al-Qaeda leader to stage attacks on Americans.
Sulaiman Abu Ghaith, reportedly a 47-year-old Kuwaiti and allegedly one of the chief propagandists of the Al-Qaeda network, stands accused of having "conspired, confederated, and agreed to kill nationals of the United States," according to a Justice Department indictment.
Attorney General Eric Holder said the arrest showed that the United States would never relent in its pursuit of the militants who launched the September 11, 2001 attacks on New York and Washington that killed nearly 3,000 people.
"No amount of distance or time will weaken our resolve to bring America's enemies to justice," Holder said.
"To violent extremists who threaten the American people and seek to undermine our way of life, this arrest sends an unmistakable message," he said.
"There is no corner of the world where you can escape from justice because we will do everything in our power to hold you accountable to the fullest extent of the law."
His capture is unusual as President Barack Obama's administration has focused on killing Al-Qaeda figures in bombing raids using unmanned drone aircraft, mostly in Pakistan's tribal belt.
A Turkish newspaper had reported earlier that Ghaith was seized by US authorities at a luxury hotel in Ankara last month and was deported to Jordan, before being taken to the United States.
But FBI, White House and CIA officials declined to comment on how Bin Laden's son-in-law ended up behind bars on American soil.
Republican lawmakers immediately denounced the Obama administration for not sending the suspect to the US-run prison at Guantanamo Bay, Cuba, where he could be held indefinitely and prosecuted under special military tribunals.
"When we find somebody like this, this close to bin Laden and the senior Al-Qaeda leadership, the last thing in the world we want to do, in my opinion, is put them in a civilian court," said Republican Senator Lindsey Graham.
"This man should be in Guantanamo Bay."
The chairman of the House Intelligence Committee, Mike Rogers, agreed.
"Al Qaeda leaders captured on the battlefield should not be brought to the United States to stand trial. We should treat enemy combatants like the enemy -- the US court system is not the appropriate venue," Rogers said.
Officials, who spoke on condition of anonymity, indicated to AFP the FBI took the lead role in the capture, as part of a multi-agency body, the High-Value Detainee Interrogation Group.
The White House set up the group after Obama shut down a controversial CIA program that had detained suspects in a network of secret prisons during George W. Bush's presidency.
US authorities accuse Ghaith of assisting Bin Laden, the Al-Qaeda chief who was gunned down in a 2011 raid by American Navy SEAL commandos, and of taking to the airwaves to promote Al-Qaeda's war against America after the 9/11 attacks.
Ghaith "held a key position in al Qaeda, comparable to the consigliere in a mob family or propaganda minister in a totalitarian regime," said George Venizelos, the assistant director-in-charge of the FBI's New York field office.
"He used his position to persuade others to swear loyalty to Al-Qaeda's murderous cause. He used his position to threaten the United States and incite its enemies."
According to the indictment, he allegedly threatened Americans, warning them that a "great army is gathering" and "the storms shall not stop, especially the airplanes storm."
The indictment also stated Ghaith was "smuggled successfully from Afghanistan into Iran" in 2002.
Ghaith is one of a number of Al-Qaeda militants who were known to be in Iran after the 9/11 attacks, but their precise status -- and whether they were placed under house arrest by the Iranian authorities -- has remained unclear.
Kuwait had stripped Ghaith of his citizenship a month after the 9/11 attacks, after he had appeared in widely circulated videos vowing more bloodshed against the United States and its allies.
He first rose to prominence during the short-lived Iraqi occupation of Kuwait in 1990-91, calling for attacks on Saddam Hussein's regime. He was later banned from preaching in Kuwait as his criticism shifted to the Kuwaiti government and other Arab countries.