Here are new details about the bomb plot thwarted in Jordan; the plot apparently involved some sort of deadly gas.

Al-Qaeda-linked terrorists planned a chemical attack on Jordan’s spy headquarters that could have killed 20,000 people, officials have said.

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”.