Islamic militants planned to detonate an explosion that would have sent a cloud of toxic chemicals across Jordan, causing death, blindness and sickness, a chemical expert has testified in a military court.

Col. Najeh al-Azam was giving evidence, on Wednesday, in the trial of 13 men who are alleged to have planned what would have been the world's first chemical attack by the al-Qaida terror group. The accused include al-Qaida's leader in Iraq, Abu-Musab Al-Zarqawi, and three other fugitives who are being tried in absentia.

Jordanian security services foiled the plot in April last year. Jordanian officials say that had it been carried out, thousands of people would have died.

Azam, a chemical expert at Jordan's General Intelligence Department, testified that a large quantity of plastic containers seized from the defendants contained hydrogen peroxide. He said the accused planned to add 'ground black cumin' to the concentrated solution, which would have made "an explosive substance stronger than TNT."

"They sought to disperse poisonous gases which would have caused death, illnesses and blindness," Azam testified.

He said his information was based on the steps to manufacture the chemical explosion as given in the confession of prime defendant Azmi al-Jayousi. Al-Jayousi has told the court his confession was extracted under duress.

Al-Azam said the defendants also had oxygen, sulfuric acid and nitroglycerin. "These are highly combustible substances which the defendants had planned to use to cause explosions that would have dispersed the toxic chemicals," he said.