The appearance of soldiers equipped against chemical warfare has caused terror in Najaf, where there are well-founded fears that the government is prepared to use poison gas against them if there is any sign of an uprising. A traveller who left Najaf recently said: "Everybody was so frightened when they saw the chemical warfare suits that they locked themselves in their houses. The streets were empty."
Iraq has used chemical weapons against domestic opponents in the past. In 1988Iraqi artillery and aircraft used munitions filled with the nerve gases sarin and tabun against the Kurdish town of Halabja, killing 5,000 people.
Iraqi troops equipped with tanks and multiple rocket launchers have sealed off Najaf since 19 February, when Ayatollah Mohammed Sadeq al-Sadr, a popular leader of the Shia Muslims, who are a majority in Iraq, was shot dead in an ambush with his two sons. He is widely believed in Iraq to be the latest victim of government death squads, who are alleged to have killed four senior members of the Shia clergy in the past five years.
The Iraqi government is aware that any sign that it is about to use poison gas - such as troops wearing chemical warfare suits - provokes terror among Iraqis. In 1991 Iraqi helicopters dropped flour, which looks like a cloud of gas, on the Kurds, in response to their uprising, to speed up their flight to Turkey and Iran.
Opponents of the Baghdad regime living in exile say that President Saddam has chosen this moment to increase repression against the Shia because he knows international attention is focused on Kosovo. Yusuf al-Khoie, a member of a Shia charitable organisation in London, says: "I have seen nothing as bad as this since the uprising after the Gulf War [in 1991]. There are many arrests and executions. Saddam knows the attention of the world is focused elsewhere."
The Shia make up 55 per cent of the Iraqi population but are excluded from power. President Saddam appears to consider the Shia's religious leaders, most of whom live in the holy cities of Najaf, Kufah and Karbala on the Euphrates, as being the most dangerous potential rebels to his rule.
Ayatollah Sadr built up a religious organisation throughout southern Iraq and in Baghdad. Before his murder he appointed community judges and prayer leaders, many of whom have now been arrested.
Iraqi security has such a tight grip on Najaf and the other holy cities that it is unlikely anybody other than government death squads could have carried out the assassinations of Sadr and the other senior clerics.
An Iraqi who left Najaf 10 days ago says the government's claim to have caught and executed the killers "is only good for Iraqi propaganda outside Iraq. Nobody believes it at home."
The Baghdad government has, however, taken advantage of the assassinations by using them as an excuse to place surviving Shia leaders under virtual house arrest, ostensibly for their own protection. Armed Iraqi security men now prevent visitors from seeing the Grand Ayatollah Ali Sistani.
Meanwhile, the US and British governments are seeking to remould the Iraqi opposition at a two-day meeting at a hotel in Windsor, Berkshire, which started yesterday. The meeting is of the Iraqi National Congress (INC), the deeply divided umbrella organisation of the opposition, and is to set a date for its general assembly, possibly later in the month.
Hoshyar Zibari, a leader of the powerful Kurdistan Democratic Party, which belongs to the INC, says the aim is to choose a new leadership. The White House, US State Department and the CIA are eager to remove control of the INC from its leader, Ahmad Chalabi, who has strong support in the US Congress.
Mr Chalabi advocates a guerrilla war using promised US equipment in the hope of provoking mutinies within the army. Mr Zibari said he sees the future of the INC as a political organisation and not as a military movement.
The Kurdish parties are unlikely to agree to the INC operating from Kurdistan, the only part of Iraq outside the control of President Saddam, unless they receive cast-iron assurances from the US that it will protect them in the event of an Iraqi counter-attack. Kurdish misgivings about US air support have been compounded by its failure to prevent Serbia expelling the Kosovars.