Kabul - The Taliban claimed responsibility on Thursday for a suicide bombing at a base in eastern Afghanistan that killed eight American civilians and one Afghan, the worst loss of life for the US in the country since October.

A US congressional official said CIA employees were believed to be among the victims.

Four Canadian soldiers and a journalist were also killed on Wednesday by a roadside bomb in Afghanistan's south, the bloodiest single incident suffered by that country's military this year.

Taliban spokesman Zabiullah Mujahid said that a Taliban bomber wearing a military uniform and a suicide vest had entered the base in Khost province on Wednesday evening and had blown himself up inside the gym.

A US official who was briefed on the blast also said it had taken place in the gym.

The official said eight US civilians and one Afghan had been killed. It was not clear if the Afghan victim was military or civilian. Six Americans had been wounded.

Nato said only that the base was used by provincial reconstruction teams, which consist of both soldiers and civilians, and other personnel.

In Kabul, a spokesman for the international coalition force in Kabul said no US or Nato troops had been killed in the afternoon explosion. The attack was the bloodiest day for Americans since eight soldiers were killed in an insurgent attack on a base in eastern Afghanistan on October 3.

In the south, Nato said that the four Canadian troops and a reporter embedded with their unit had died when their armoured vehicle hit a bomb while on an afternoon patrol south of Kandahar city. It was the third-deadliest day for Canadians in Afghanistan since the war began.

Michelle Lang, a 34-year-old health reporter with the Calgary Herald, was the first Canadian journalist to die in Afghanistan. Lang arrived in Afghanistan just two weeks ago.

"She was one of those journalists who always wanted to get to the bottom of every story so this was an important trip for her," said her Calgary Herald colleague Colette Derworiz.

The military has not disclosed the names of the Canadian troops because relatives had not all been notified.

"We are all very saddened to hear this tragic news," Alberta Health and Wellness Minister Ron Liepert said in a statement. "Michelle covered health issues with professionalism, accuracy and thoroughness. She was tenacious in her quest to inform Albertans, and for her diligence she was very well respected."

Brigadier General Daniel Menard, commander of coalition forces in Kandahar, said that the soldiers had been conducting a community security patrol in order to gather information about daily life in the area and how to maintain security.

Wednesday was the second lethal strike against the Canadian force in a week. One Canadian soldier and an Afghan soldier were killed December 23 during a foot patrol in Panjwayi district of Kandahar province.

According to Associated Press figures, the latest casualties bring to 32 the number of Canadian forces killed in Afghanistan this year; in all, 138 have died in the war.

Separately on Wednesday, Nato questioned Afghan reports that international troops had killed 10 civilians, including schoolchildren, in a weekend attack that prompted hundreds of angry Afghan protesters to burn an effigy of US President Barack Obama and chant "death" to America.

The head of an investigative team appointed by Afghan President Hamid Karzai said that eight students between the ages of 12 and 14 had been among the dead discovered in a village house in a remote section of the province of Kunar in eastern Afghanistan.

Nato said in a statement released late on Wednesday night that while there was no direct evidence to substantiate the claims, the international force had requested and welcomed a joint investigation to reach an "impartial and accurate determination" of what had happened in the attack.

Conflicting accounts of what occurred during fighting in Kunar's Narang district prompted an emotional outcry over civilian deaths, one of the most sensitive issues for international troops fighting the more than eight-year-old war.

Although insurgents are responsible for the deaths of far more civilians, those blamed on coalition forces spark the most resentment and undermine the fight against militants.

With 37 000 more US and Nato troops being deployed to the battle zone, concern over civilian casualties is unlikely to ease anytime soon.

Several hundred Afghans demonstrated in the capital of Kabul and in the eastern city of Jalalabad, where the likeness of Obama, adorned with a small American flag, burned on a pole held above demonstrators. - Sapa-AP