Khalil al-Dulaimi, the head of the team, accused the US led "occupation forces" of responsibility for the killing and said he and his colleagues felt unable to continue due to daily threats which was preventing them from going to their offices and interviewing witnesses.
The defence lawyers declared that they consider the projected reopening of the trial, on 28th November, "null and void" and maintained that only a "direct, neutral international intervention" will guarantee security.
The Iraqi government, and US Justice Department lawyers advising them, have rejected calls for the case to be heard in another country or before an international tribunal.
Officials insisted that the trial will go ahead as planned and said that the court will take it upon itself to appoint a new legal team if the current one fail to appear.
However, such a move will further dent the credibility of the legal process. Although Iraqi law allows the court to appoint defence lawyers, the practice was widely criticised by Western governments and human rights groups when it took place under Saddam Hussein's regime.
The boycott call comes after gunmen killed Adel al-Zubeidi, the lawyer for former vice-president Taha Yassin Ramadan, and injured Thamir al-Khuazale, representing Saddam's half brother Barazan Ibrahim, in an ambush.
Last month, just days after the trial had begun, another defence attorney, Saadoun al-Janabi, was shot dead. Those involved with the case killed so far also include one of the judges and his son; the brother of the chief prosecutor, Jaafar al-Mousawi and three other court officials.
The five judges trying the case said yesterday that it will give a ruling in the near future. Rizgar Mohammed Amin, a Kurd, who presided over the first day of the case, said "We are five members if the court and now is the time to sit down and talk and discuss this among us so we can reach a decision in the coming days."
The United Nations Secretary General, Kofi Annan, said in a statement, "It is vitally important that security of all involved with the tribunal be equally assured to ensure a fair trial free from intimidation and coercion."
Iraq's president, Jalal Talabani, condemned the latest assassination and urged the remaining defence lawyers to accept the offer of government protection which they have refused so far.
However, Mr Dulaimi responded, "It is the Interior Ministry that has offered to provide us with protection against these attacks, but it is the Ministry itself that is planning the killings.
"The occupation forces are responsible for this criminal incident, and they bear the responsibility of preserving the lives of the people regardless of their identity."
Meanwhile violence continued across the country yesterday. Seven policemen were killed and five others injured when a suicide car bomb struck a patrol near Baqouba, 35 miles northeast of Baghdad. A driver for the Sudanese embassy was shot dead in Baghdad and an US Marine was killed by a roadside bomb in western Iraq bringing the number of US servicemen killed to 2,055.Reuse content