Enemy mortar fire caused a munitions dump explosion in Iraq that killed six European soldiers who were defusing Saddam-era ordnance, a special military commission said Wednesday.

One Latvian and three Slovakian and two Polish soldiers were killed in the explosion near the city of Suwariyah (search) on Tuesday.

"The deaths did not result from any inappropriate action during the defusing, but it was the result of a mortar attack," said Gen. Piotr Czerwinski, the head of a special commission that investigated the accident.

The soldiers were killed when a pile of some 100 anti-tank and 300 smaller shells that were to be destroyed exploded. Another Polish soldier, heavily burned in the explosion, was flown to a specialized hospital in Homburg, Germany, for treatment.

It is not known who was responsible for the attack, Czerwinski told a news conference in Iraq broadcast on Polish television.

Maj. Gen. Mieczyslaw Bieniek, commander of the Polish-led multinational force in south-central Iraq, said he suspected involvement of former Iraqi soldiers because of the attack's location and precision.

"There was an artillery school in the region and many officers ... having no occupation now, offer their services to the terrorists," he said.

The multinational camp in the area has been fired on frequently. The last mortar attack took place Friday.

Czerwinski said investigators found three 82mm mortar craters near the site of the explosions, and estimated that the rounds were fired from one to two miles away.

He said four rounds were thought to have been fired, one of which hit the pile of shells.

Witnesses reported hearing the distinctive whistling of incoming mortar fire, and then a series of explosions over 15 minutes, he said.

The soldiers killed were the first in Iraq for both Slovakia and Latvia, while Poland has now suffered six military deaths.

Poland has 2,400 soldiers in Iraq, leading a multinational force that totals 6,200 troops.

Slovakia has 105 soldiers in Iraq, mostly for demining work. Latvia, which joined NATO last month, has 116 soldiers in Iraq, most of them serving alongside Poles.