Al-Qaeda-linked terrorists planned a chemical attack on Jordan's spy headquarters that could have killed 20,000 people, officials have said.
Officials say materials for a chemical bomb have been found
Earlier this week King Abdullah said a massive attack had been thwarted by a series of arrests, but named no target.
Now unnamed officials say the suspects have confessed to plotting to detonate a chemical bomb on the Amman HQ of the Intelligence Services.
The plot was reportedly hatched by al-Qaeda suspect Abu-Musab al-Zarqawi.
Washington has accused the 38-year-old Jordanian radical of masterminding a string of spectacular suicide bombings in Iraq.
An official involved in the inquiry in Jordan told AFP news agency: "We found primary materials to make a chemical bomb which, if it had exploded, would have made nearly 20,000 deaths ... in an area of one square kilometre.
"The target of this bomb was the headquarters of the
Intelligence Services," situated on a hill in the western suburb of Amman, he added.
The official said another operation planned by the network was to use "deadly gas against the US embassy and the prime minister's office in Amman ... and other public buildings in Jordan".
On Tuesday, in a letter thanking his intelligence chief for uncovering the plot, King Abdullah said Jordan had "lived through an extremely delicate situation in recent days".
"But divine protection has thwarted the plans of these criminals and saved the lives of thousands of civilians in what would have been a crime never before seen in the kingdom," he argued.
The intelligence chief General Saad Khair said the group used religion as a pretext for its actions, but their plans were anything but religious.
He thought that they wanted to attack Jordan's position on upholding Arab causes, especially Palestinian rights. He said mop-up operations were continuing.
Two weeks ago the authorities in Jordan said they had found cars carrying explosives by an underground group planning to attack US interests in the kingdom.