Three Canadian soldiers have been killed by an explosion in southern Afghanistan.

They were travelling in an open-topped, unarmoured vehicle when it was struck by an improvised explosive device, said Brig.-Gen. Tim Grant at a press conference Wednesday at Kandahar Air Field.

The soldiers have been identified as Cpl. Stephen Frederick Bouzane, 26; Pte. Joel Vincent Wiebe, 22; and Sgt. Christos Karigiannis (age not immediately available).

All three were members of 3rd Battalion Princess Patricia's Canadian Light Infantry, based in Edmonton.

The three victims were the only occupants of an M-Gator -- a six-wheeled, all-terrain vehicle, which was part of a resupply convoy between two checkpoints less than a kilometre apart. Grant described the vehicle as "much like a John Deere tractor you would get back home."

He said the military will reassess its use of the vehicle.

"This is an unfortunate accident. We will review our procedures and if we determine we need to change them we will do so," said Grant.

"But at the current time we look at this as an unfortunate accident."

Grant said the military has lost three good friends who believed in their mission. He said NATO operations have left the Taliban disorganized and unable to mount "a concentrated force of great threat," and as a result they are falling back on guerrilla tactics such as roadside bombs.

"What we're seeing is continued attacks by what really is a disrupted enemy. There is no doubt that the suicide attacks will continue, roadside bombs will continue, but we believe our operations continue to disrupt them and continue to ensure they cannot gather, concentrate and continue to pose a threat to the people of Afghanistan," he said.

CTV's Paul Workman, reporting from Kandahar, said commanders obviously thought the area was safe enough to use such an exposed vehicle on a resupply mission.

"It seems likely that Taliban fighters were watching the Canadians and saw an easy target -- an open vehicle with no armour and soldiers who were more or less defenceless against a hidden roadside bomb."

Soldiers often use the M-Gator to transport small loads such as luggage, cots, boxes of water, and construction materials.

MPs pay respect

A report says Cpl. Bouzane was born in Newfoundland and grew up in Scarborough, Ont., east of Toronto. Bouzane's sister, Kelly, described her brother as a quiet and reserved young man who was in Afghanistan "to make a difference."

She told the Canadian Press that her brother went to Afghanistan for his first tour in February. She last saw him at Christmas.

The Canadian Press reports that Wiebe, 22, had a fiancee in Edmonton where his regiment is based.

In the House of Commons, Prime Minister Stephen Harper called the incident a "terrible tragedy." He described the soldiers as brave people who put on uniforms to defend the freedoms of people around the world.

Liberal Leader Stephane Dion said the three fallen heroes, along with their comrades, served with courage and honour.

The death toll for Canadian military personnel in Afghanistan has now reached 60.

These deaths come on the same day as the funeral for 25-year-old Trooper Darryl Caswell in Bowmanville, Ont.

Caswell was also killed by a roadside bomb on June 11.

Ongoing violence

In a separate clash Wednesday, The Canadian Press reports that Canadian and Afghan soldiers killed 15 insurgents in a four-hour running firefight in the southern Zhari district.

Two Canadians and three Afghan soldiers suffered minor injuries in the battle.

India Company's commanding officer Maj. Dave Quick told CP that troops battled militants in compounds and farmers' houses, and eventually called in air support.

The goal of the assault was to disrupt the Taliban presence and put an end to attacks on Afghan police using a nearby highway, Quick said.

In other violence, officials said earlier Wednesday that gunmen fired on people praying in a mosque in eastern Afghanistan, killing three.

The attack took place in Ismail Kheil, a village in Khost province. Two armed men entered the mosque and opened fire, killing three and wounding a fourth, according to Wazir Pacha, a Zabul province police chief who spoke to AP.

The attackers fled the scene, and police are still unsure of the motive.

In another attack, militants ambushed a United Nations convoy on the main highway between Kabul and Kandahar. The strike left two Afghan guards dead, and a third wounded. Two UN vehicles were damaged in the attack, Jailani Khan, a local police chief told AP.

And in the southern Kandahar province, Afghan police clashed with militants, retaking control of Miya Nishin district. One day earlier, militants overran the district. But just hours after police established control the insurgents once again took over the district, said Esmatullah Alizai, a provincial police officer.

Fierce fighting has reportedly raged since Saturday in Uruzgan province, a mountainous region that borders Kandahar.

More than 100 people, including dozens of civilians, have reportedly been killed in the clashes.

About 2,400 people have been killed so far this year in Afghanistan, including civilians, militants and troops, according to an AP tally.

Though there appears to have been an upsurge in Taliban activity in recent weeks, NATO officials say it was expected.

"We find ourselves in the midst of the so-called fighting season, when what we had predicted is taking place: an increase in suicide bombings and more desperate attempts by the enemies of peace and stability to present the illusion that they are stronger than they are," said Lt. Col. Maria Carl, spokeswoman for NATO's International Security Assistance Force.

An umbrella group representing 94 aid agencies working in Afghanistan -- both foreign and Afghan -- warned Tuesday that goodwill toward foreign fighters has eroded in the five years since the Taliban was ousted from power.

The deterioration is mainly the result of botched raids and air strikes by U.S. and NATO troops, stated the ACBAR umbrella group.

With files from The Associated Press and The Canadian Press