Afghanistan on Wednesday executed six "criminals and terrorists", an official said, a day after eight other death row prisoners were hanged in rare mass executions in the war-wracked country.

The Taliban, which is leading an insurgency against the Western-backed government, had warned there would be reprisals if any of their militants were executed.

President Hamid Karzai approved the executions of the six who were sentenced to death "on charges of terror, conducting attacks, explosions and organising suicide attacks", a government spokesman said in a statement.

The Taliban, who are fighting Karzai's government and 100,000 NATO troops, said if what they called "prisoners of war" were executed there would be "heavy repercussions" for government officials.

It urged the United Nations, the Organisation of the Islamic Conference, the Red Cross and international rights groups to prevent the executions.

The Taliban, ousted from power by a US-led invasion in 2001, were notorious for executing people in public for "crimes" including adultery. The executions were often carried out at half-time during games in the main football stadium in Kabul.

The European Union and international rights groups condemned Afghanistan's execution of the first eight prisoners -- described as murderers, kidnappers and rapists -- and urged Kabul to drop plans to hang any more.

"The Afghan government should end its sudden surge of executions and institute a moratorium on further executions," Human Rights Watch said.

"The weakness of the Afghan legal system and the routine failure of courts to meet international fair trial standards make Afghanistan's use of the death penalty especially troubling," it said.

Amnesty International said "the sheer number of people who could be killed by the state is a particularly shocking use of what is the ultimate cruel and inhuman form of punishment".

The EU mission in Afghanistan called on the government to commute all death sentences and to reintroduce a moratorium on executions as a first step towards abolishing capital punishment.

The government's emailed statement attached pictures of the men who were hanged and a description of the crimes for which they were convicted.

Three of the men were found guilty of organising suicide attacks in Kabul that killed eight people, two for murdering two Afghan UN employees and one for killing three provincial education officials and eight border police.

The Kabul attacks included the deaths of two foreigners and a young Afghan girl in Kabul's famed Chicken Street, a popular shopping area for expatriates, the statement said.

It was not immediately clear when the attacks took place or how long the men had been on death row.

Executions have been infrequent since the fall of the Taliban Islamist regime in 2001, but have several times involved multiple deaths. Since 2001 there had been four sets of executions.

One man, Abdullah Shah, was executed in 2004 for murder, 15 were killed by firing squad in October 2007 and seven in 2008. Last year, two Taliban militants were executed for an attack on a bank that left 38 people dead.

Amnesty International said some 200 prisoners are reportedly on death row in Afghanistan.

A military court on Monday rejected an appeal by an Afghan soldier sentenced to death for killing five French troops in an insider attack in January - the first such conviction for a so-called 'green-on-blue' attack, but he was not among those executed.

The foreign ministry in France, which does not use the death penalty, said at the time said it "took note" of the sentence, adding its thoughts were with the soldiers who were killed and their families.