"A credible appeals process is an essential part of fair-trial guarantees," Arbour, the UN's high commissioner for human rights, said in a statement.

"This is particularly important in this instance, in which the death penalty has been imposed," she said.

"Guaranteeing the right of a fair trial of persons accused of major human rights violations is key to consolidating and strengthening the very important process of ensuring justice and countering impunity that Iraq has embarked upon."

"Those convicted today should have every opportunity to exhaust their appellate remedies in a fair way, and whatever the outcome of an appeal, I hope the government will observe a moratorium on executions," she added.

Meanwhile, Switzerland on Sunday also criticized the death penalty against Saddam Hussein.

"Former Iraqi President Saddam Hussein deserves a harsh punishment for his serious crimes," a statement by the Swiss Foreign Ministry said.

But the death penalty, which is outlawed in the Swiss constitution, is not an acceptable form of punishment, the statement said.

Switzerland is active in calling for the abolition of the death penalty worldwide.

Saddam was sentenced to death by hanging by a court in Baghdad on Sunday. He had been convicted over the killing of 148 people in the mainly Shia town of Dujail following an assassination attempt on him in 1982.

Saddam and his co-defendants have the right to appeal against the sentence by a court in Baghdad.