Kabul - Three Canadian soldiers with the NATO-led security forces in Afghanistan and four Taliban militants were killed in the country's south, while Afghan authorities were investigating the deaths of eight prisoners in country's largest prison, officials said Saturday.

The soldiers, serving under the banner of UN-mandated International Security Assistance Force (ISAF), were killed in a roadside bomb blast in southern province of Kandahar on Friday, the Canadian Defence Ministry said in a statement.

ISAF in Kabul confirmed the deaths of the soldiers, saying, "these soldiers died honourably, helping bring security to Afghanistan."

Around 2,500 Canadian soldiers are stationed in the southern province of Kandahar, once the headquarters for the fugitive Taliban leader, Mullah Mohammad Omar.

The Canadian soldiers are part of a force of 65,000 international troops, deployed to Afghanistan from 40 nations following the 2001 ouster of regime of the Islamist extremist Taliban.

Also in Kandahar, two militants trying to plant roadside bombs were killed on Friday when their explosives exploded prematurely, the Afghan Interior Ministry said in a statement.

Two other militants were killed and five were wounded in a US-led coalition operation in Zerok district of the south-eastern province of Paktika on Friday, the US military said in a statement.

Meanwhile, Afghan officials were investigating the facts surrounding an incident on Friday in Puli Charkhi prison in outskirts of Kabul that resulted in the deaths of eight prisoners and left ten other prisoners and three guards wounded.

"We have launched an investigation to find out what caused the clash between the prisoners and the guards, and whether the prisoners were killed by gunshot or something else, " said Mohammad Qasim Hashimzai, the Afghan deputy justice minister.

Hashimzai said that the police had information that some of the prisoners had contacts with militants outside the prison and wanted to plot a jailbreak.

The police forces went inside the cells to look for mobile phones and weapons, but faced resistance by the prisoners, he said, adding that the forces opened fire on prisoners when the guards were attacked.

In June the Taliban launched an attack on a prison in southern province of Kandahar that helped some 900 prisoners, with almost half of them jailed Taliban fighters, to escape. (dpa)