British soldiers and Iraqi police clashed Saturday with armed, stone-throwing protesters in southeastern Iraq, killing six people. U.S. officials acknowledged American soldiers mistakenly killed two Iraqi policemen after they failed to identify themselves to a patrol.

In Baghdad, a senior U.S. military officer confirmed that preliminary reports showed that a U.S. Army medevac helicopter that crashed last week near Fallujah (search), killing all nine soldiers aboard, was shot down.

Also Saturday, Danish and Icelandic troops found a cache of 36 shells in southern Iraq, and preliminary tests showed they contained a liquid chemical weapon, the Danish military said.

But U.S. Brig. Gen. Mark Kimmitt said the leaking shells, found near Al Quarnah, north of the city of Basra (search), are believed to date from the Iran-Iraq war, which ended in 1988.

A statement from the Danish army said British experts did a preliminary test and said the shells contained "blister gas (search)," but did not elaborate.

The statement did not specify the type of gas, but before the war, the United States alleged Iraq still had stockpiles of mustard gas (search), a World War I-era blister agent that is stored in liquid form.

Allegations that Saddam maintained chemical and other weapons of mass destruction in violation of U.N. orders was cited by the United States as the main reason for launching the Iraq war. No such weapons have yet been found.

Meanwhile, a U.S. military spokesman said that two Iraqi policemen were shot Friday after paratroopers from the 173rd Airborne Brigade responded to a report of "family fighting" in Kirkuk, about 150 miles north of Baghdad.

Paratroopers spotted two men firing into a house, said Maj. Josslyn Aberle, a spokeswoman for the 4th Infantry Division. The men, who were wearing long coats, fled as the troops approached and were joined by a third man, she said.

"The soldiers verbally warned the three to stop and then fired warning shots," Aberle said. "The men refused to comply and the soldiers took a defensive position and fired," killing two of them and detaining the third.

All three were found to be Iraqi policemen, Aberle said. The U.S. military is investigating why they refused to identify themselves.

Saturday's trouble in Amarah, 200 miles southeast of Baghdad, started when hundreds of Iraqis angry over the lack of jobs in town gathered in front of the office of the U.S.-led coalition to demand work.

As the protesters grew agitated, shots rang out from the crowd, a British military spokeswoman said. At the same time, she said troops "received reports of small explosions in the crowd."

Iraqi police, believing they were under attack, opened fire into the crowd but did not hit any of the protesters, she said. But witnesses said the police killed some of the protesters.

British soldiers moved in with armored vehicles to support the police, and protesters hurled at least three explosive devices at them, she said.

One man "who was in the process of throwing a device" was shot dead by the soldiers, the spokeswoman said.

The crowd dispersed but later some of them returned and lobbed two explosive devices at the armored cars. Soldiers shot one of the attackers and apparently wounded him, she added. Three other devices were thrown at the soldiers before tensions eased.

Six people were killed and at least 11 wounded, according to Dr. Saad Hamoud of the Al-Zahrawi Surgical Hospital. The British said they had reports of five deaths and one injury. There were no casualties among police or soldiers.

In Baghdad, U.S. Brig. Gen. Mark Kimmitt told reporters that reports indicate the Black Hawk (search) medevac helicopter that crashed Thursday south of Fallujah was probably brought down by ground fire.

Iraqi witnesses said they saw a missile strike the second of two medevac helicopters as they flew over an area known for resistance against to the U.S.-led occupation.

The nine deaths aboard the helicopter brought to 494 the number of American service members who have died since the Iraq war began March 20.

In Tikrit, Saddam Hussein's hometown, the U.S. military said it was investigating allegation that U.S. troops opened fire on a taxi Jan. 3, killing four Iraqi civilians. Maj. Josslyn Aberle, a spokeswoman for the 4th Infantry Division, declined to provide any details of the investigation.

The lone survivor, Ibrahim Allawi, said troops raked his car with gunfire as he tried to pass a convoy north of the capital. Police found Allawi and the others, including a 7-year-old boy, in the bullet-riddled car.