A U.S.-led team Tuesday started a series of tests to determine whether a cluster of 36 mortar shells unearthed last week in southern Iraq contain a liquid blister agent, a Danish army official said.

Fourteen members of the Iraqi Survey Group (search), made up of intelligence analysts, interrogators and translators, will be testing the 120mm shells with a mobile laboratory at the Iraqi site over the next few days, Maj. Kim Gruenberger of the Danish Army Operational Command (search) told The Associated Press.

The U.S. military believes the shells are remnants from the 1980-1988 war between Iraq and neighboring Iran.

"They have been working since this morning," Gruenberger, who spoke from the Danish army's command center in Karup, 165 miles northwest of Copenhagen. He couldn't say when the results would be available.

Danish troops and Icelandic de-miners uncovered the shells Friday after receiving tips from local residents near Qurnah, north of the city of Basra, where Denmark's 410 soldiers are based.

Preliminary tests on the plastic-wrapped but damaged shells showed they contained a liquid blister agent.

But initial tests by field troops are designed to favor a positive reading, erring on the side of caution to protect soldiers. More sophisticated tests are often necessary.

Some Iraqis have told Danish soldiers that other mortar shells were buried in the area, including a stockpile dumped in the Tigris River that could contain as many as 400 rounds, Gruenberger said.

Danish engineers will start investigating those sites after they are done with the present case, he said.

In October, Dutch marines found several dozen artillery shells dating to the 1991 Gulf War in southern Iraq, but the shells contained no biological or chemical agents. In April, U.S. troops found a dozen 55-gallon drums in northern Iraq. Preliminary tests found possible evidence of a nerve agent and a blister agent, but later tests found the contents were not chemical weapons.

Before launching the war on March 20, the United States asserted Iraq still had stockpiles of mustard gas, a World War I-era blister agent that is stored in liquid form. The chemical burns skin, eyes and lungs.

U.S. intelligence officials also claimed Iraq had sarin (search), cyclosarin (search) and VX (search), which are extremely deadly nerve agents.

During the war, potential chemical and biological findings were sent to a U.S. government laboratory in Fort Detrick, Md. and to a British government laboratory in Portendown, Britain. In some cases, a third set was sent to the United Nations' chemical weapons watchdog agency in The Hague, Netherlands. All the tests came back negative.

Since the war ended, the U.S.-led coalition has found several caches that tested positive for mustard gas but later turned out to contain missile fuel or other chemicals.

Other discoveries early in the U.S.-led occupation turned out to be old caches that already had been tagged by U.N. inspectors and were scheduled for destruction.