The tactic was first used earlier this year in Najaf, a city close to the Euphrates, after the murder, almost certainly at the hands of a government death squad, of Ayatollah Mohammed Sadeq al-Sadr, a popular religious leader. He was shot dead with his two sons near Najaf after demanding that the government release imprisoned clergy.
His death led to the most widespread riots in Iraq since the uprisings of the Shia Muslims and the Kurds in 1991. These were crushed by Iraqi security forces who shot into crowds and carried out mass arrests. But in Najaf, a city holy to the Shia, who make up 55 per cent of the Iraqi population, the government found a simpler way of preventing rebellion.
After the assassination of Ayatollah al-Sadr regular Iraqi troops and security men sealed off Najaf, dominated by the great golden dome of the shrine-tomb of Imam Ali, a founder of the Shia faith. Now a resident of the city, who left Iraq at the end of last month, has spoken for the first time about the events immediately following the murder.
After four gunmen killed the Ayatollah in his car late on a Friday evening, people rushed to the hospital where he had been taken. They met two doctors who were crying. "Al-Sadr is dead," said the doctors, "but although his two sons are alive, security won't let us treat them." Some 150 people broke down an outer door of the hospital, but were confronted by Brig Gen Sami, the head of local Iraqi security in Najaf, whose men forced the crowd to disperse.
Iraqi troops poured into Najaf along with units of the Fedayeen Saddam, a heavily-armed and ferocious militia force created by the Iraqi leader. Ayatollah al-Sadr was buried before sunrise on Saturday to prevent demonstrations at his funeral.
The city was on the verge of rebellion, but in the early morning light people saw that new detachments of security men were appearing near the shrine of Imam Ali. "For the first time we saw people in white uniforms with gas masks," said one witness. "I had been in the army and I realised immediately that they were wearing chemical warfare equipment. Everybody in Najaf thought they were about to use poison gas on us."
It was not an unwarranted suspicion. In 1988, at Halabja in Iraqi Kurdistan, Iraqi artillery and aircraft used shells and bombs containing sarin and tabun nerve gas on the city. Some 5,000 people were killed. The Iraqi army used mustard gas in the war with Iran, and 50,000 former Iranian soldiers still suffer from the after-effects of poisoning.
Fear that chemical weapons were about to be used on Najaf increased when terrified local security men began to beg people not to cause trouble. They said the men in chemical warfare suits came from an emergency detachment of the Amn al-Khas, the elite presidential security organisation.
The tactic worked because terror of chemical weapons is ingrained in Iraqis. Nobody in Najaf wanted to find out the hard way if they were really going to be used. Although Najaf was full of religious students loyal to Ayatollah al-Sadr, there was no uprising. People retreated to their houses and all shops were closed for a week, at the end of which the chemical warfare troops again paraded through the streets.
This was in sharp contrast to other Shia districts in Iraq. There were violent riots in Nassariyah and al-Thawra district (now named Saddam City), a Shia working-class neighbourhood in Baghdad. The government struck back by arresting clergy and religious judges appointed by Ayatollah al-Sadr.
Bizarrely, at the same time as it threatened the people of Najaf with a gas attack, the government offered them a concession. Najaf had received only an intermittent supply of electricity. But in the aftermath of the assassination Najafis noticed they had electricity all day. Even so the city re- mained sealed off, ringed by tanks, rocket launchers and artillery.
President Saddam has always taken the threat of a Shia rebellion more seriously than other forms of opposition. The senior Shia clergy have a mass following, and unlike other opponents, they are inside the country. In the past five years senior Shia clerics have been all but eliminated by an assassination campaign, probably carried out by the Iraqi security forces.
In recent weeks repression in southern Iraq has reached new heights, with continuing arrests and executions. Here the Iraqi government has had a stroke of luck. President Saddam appears aware that the eyes of the world are on Kosovo. The journalists who once crowded the al-Rashid hotel in Baghdad are now all in the Balkans.
In the eyes of the US, Slobodan Milosevic of Serbia has replaced the Iraqi leader as the chief international demon. With his own people under control, Saddam is now in a better position than ever to bring an end to the isolation of Iraq, which has lasted since the Gulf War.