NEW YORK — Tests of the artillery shell that detonated in Iraq on Saturday have confirmed that it did in fact contain an estimated three or four liters of the deadly sarin (search) nerve agent, Defense officials told Fox News Tuesday.

The artillery shell was left as a roadside bomb, the U.S. military said Monday.  Two U.S. soldiers were treated for minor exposure to the nerve agent when the 155-mm shell exploded before it could be rendered inoperable.

The soldiers displayed "classic" symptoms of sarin exposure — most notably dilated pupils and nausea, officials said.  The symptoms ran their course fairly quickly, however, and as of Tuesday, the two had returned to duty.

A shell filled with mustard gas (search) that was part of an improvised explosive device (IED) was also discovered on May 2, Defense officials said.

That shell was found by passing soldiers in a median on a thoroughfare west of Baghdad.  The most likely way it got there was that it was simply left there by someone, officials said, but it's unclear whether it was meant to be used as an IED.

Testing done by the Iraqi Survey Group (search) — a U.S.-organized group of weapons inspectors who have been searching for weapons of mass destruction (search) since the ouster of Saddam Hussein — concluded that the mustard gas was "stored improperly" and so the gas was rendered "ineffective."

"It's not out of the ordinary or unusual that you would find something [like these weapons] in a haphazard fashion" in Iraq, Edward Turzanski, a political and national security analyst, told Fox News on Tuesday.  But "you have to be very careful not to be entirely dismissive of it … it remains to be seen whether they have more shells like this."

Iraq: A 'Bazaar of Weapons'

New weapons caches are being found every day, experts said, including "hundreds of thousands" of RPG rounds and man-portable air defense weapons used to shoot down coalition aircraft.

"Clearly if we're gonna find one or two of these every so often — used as an IED or some other way — the threat is not all that high but it does confirm suspicion that he did have this stuff," said Ret. U.S. Army Col. Robert Maginnis.

"It is a bazaar of weapons that are available on every marketplace throughout that country," Maginnis added.   "We're doing everything we can to aggressively disarm these people but there were so many things that were stored away by Saddam Hussein in that country … it's a huge job that we're tackling."

Some are concerned that enemy fighters with access to potentially lethal weapons in a country full of stockpiles could mean more risk to coalition forces and Iraqis.

"What we don't know is if there are other shells, which there certainly could be," said Dennis Ross, a former ambassador and special Middle East coordinator and a Fox News foreign affairs analyst.  "We also don't know whether or not these kind of shells could be used as explosives, which could have a more devastating effect on our troops."

But some experts say that the individual shells themselves don't pose a threat to the masses.

"I'm not as concerned they're going to use a lot of chemical munitions … they're not gonna use these as improvised explosive devices because they don't have a big blast associated with them, but they do combine those two compounds into the noxious sarin gas.  But they can't do it all that well with a small explosive charge," Maginnis said.

"The reality is, they'd have to have a whole bunch of these things, have to find some way of blowing them with a large charge to even create a cloud."

But that doesn't mean insurgents won't find a better way to make the devices to create a more "terrorist-type of attack" against U.S. forces, Maginnis continued.

The task of military analysts in Baghdad is to determine how old the sarin shell is. A final determination will have a significant effect on how weapons researchers and inspectors proceed.

Some are suggesting that the unmarked shells found date back to the Persian Gulf War in the early 1990s.  The mustard gas shell may have been one of 550 projectiles for which Saddam failed to account for in his weapons declaration shortly before Operation Iraqi Freedom began.  Iraq also failed to then account for 450 aerial bombs with mustard gas.

It's not clear if enemy fighters simply found an old stockpile of weapons of if they knew what was inside.

Defense Secretary Donald Rumsfeld reacted cautiously to the news of the discoveries.

"So what we have to then do is to try to track down and figure out how it might be there, what caused that to be there in this improvised explosive device, and what might it mean in terms of the risks to our forces," Rumsfeld said Monday.

Kurds: We Have Evidence of WMD

Many have no doubt similar substances will be found as the weapons hunt continues.

"We don't know where they are but we suspect they are hidden in many locations in Iraq ... it's quite possible that even the neighboring states who are against the reform of Iraq ... are helping the Saddamites in hiding," Howar Ziad, the Kurdish representative to the United Nations, told Fox News on Tuesday.

"As we know, the Baathist regime had a track record of using" these chemicals against people in Iraq, such as the Kurds, Ziad continued.  "He's [Saddam] never kept any commitment he's ever made to the international committee nor to the people" to not use such deadly materials.

Saddam's regime used sarin in mass amounts during the Iraqi military's attack on the Kurdish town of Halabja (search) in 1988.  More than 5,000 people are believed to have died in those attacks; more than 65,000 were injured.  Sarin was also just one nerve agents used by the Iraqi Army against Iran during the Iraq-Iran War in the 1980s.

Ziad said the United Nations, World Health Organization and others haven't "bothered" to travel to the Kurdish region in northern Iraq to see the effects sarin and other deadly agents have had on people firsthand and to get proof that Saddam did in fact possess such weapons.

"We have evidence — we have victims of the use of those agents and we're still waiting for WHO and the U.N. to come investigate," Ziad said.

Fox News' Bret Baier, Mike Emmanuel and Ian McCaleb contributed to this report.