BAGHDAD, Iraq - Iraqi extremists in videotape aired today by Al-Jazeera television showed what they said was a Polish woman hostage held in Iraq and demanded that Poland remove all its troops from Iraq and that Iraqi female prisoners be released.

Meanwhile, a different militant group claimed today to have obtained a large amount of explosives missing from a munitions depot facility in Iraq and threatened to use them against foreign troops who invade Iraqi cities.

The new kidnapping drama came as deadline wound down for a Japanese hostage who was shown in a video aired Tuesday saying his captors - said to be the al-Qaida-linked militant group of Abu Musab al-Zarqawi - would behead him in 48 hours unless Japan withdraws its troops from Iraq, a demand Tokyo has rejected.

Also held since last week is humanitarian worker Margaret Hassan, an Irish-British-Iraqi woman who appeared in a video broadcast on Al-Jazeera on Wednesday pleading for Britain to act to save her life.

In new violence today, a car bomb exploded in southern Baghdad, killing a U.S. soldier and at least one Iraqi civilian and wounding two other American soldiers, the U.S. military said. At least 1,109 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

The new hostage video showed a middle-aged woman with gray hair and dressed in a polka-dotted blouse sitting in front of two masked gunmen, one of whom was pointing a pistol at her head.

The kidnappers, who called themselves the Abu Bakr al-Siddiq Fundamentalist Brigades, said the woman, who was not identified by name, was a Polish citizen working with U.S. troops in Iraq.

Interior Ministry spokesman Col. Adnan Abdul-Rahman said the woman was a longtime Iraq resident with Iraqi citizenship and was believed to have been abducted Wednesday night from her home in Baghdad. Abdul-Rahman did not release her name.

The woman's voice was not audible on the tape, but Al-Jazeera said the woman called on Polish troops to leave the country and for U.S. and Iraqi authorities to release all female detainees from the Abu Ghraib prison.

Poland commands some 6,000 troops from 15 nations - including some 2,400 from Poland - in the Babil, Karbala and Wasit provinces.

Ahmed al-Sheikh, Al-Jazeera's editor-in-chief, said the kidnappers did not mention a specific death threat or give a deadline. He would not say when or how the station obtained the tape.

Japanese leaders were trying today to win the realease of Shosei Koda, a 24-year-old Japanese tourist who appeared in a video Tuesday saying he would be beheaded in 48 hours unless Japan pulled out of Iraq. No specific time for the deadline's end today was given.

Al-Zarqawi's terror group, al-Qaida in Iraq, claimed responsibility for Koda's abduction.

Prime Minister Junichiro Koizumi, who has rejected the demand, said his government was "calling on other countries and those who sympathetic to Japan, and the Iraqi people" to help.

A Japanese government envoy arrived early today in Amman, Jordan, to coordinate diplomatic efforts to free Koda.

Koda, who left Japan in January for a yearlong trip starting in New Zealand, told people he met traveling that he wanted to go to Iraq to see the country.

"What I want Shosei's kidnappers to understand is that he is not an activist supporting the stay of the Japanese troops in Iraq nor the American policy there," said his father, Masumi, 54.

Late Wednesday, Al-Jazeera aired a video showing Hassan, the kidnapped director of CARE International in Iraq, who again pleaded with Britain to withdraw its forces from Iraq even as some 800 British troops began deploying toward the Baghdad area. She also asked for the release of Iraqi women hostages.

The soldiers of the Black Watch and the Queen's Dragoon Guards are expected to assume security responsibility in areas close to the capital to relieve U.S. troops who are preparing for a major assault on the insurgent stronghold of Fallujah and other areas west and north of the capital.

Hassan, 59, is the most high-profile of more than 150 foreign hostages who have been abducted in Iraq. At least 33 of the hostages have been killed.

No group has claimed responsibility in Hassan's abduction. But followers of Jordanian militant Abu Musab al-Zarqawi made the same demand for the release of female prisoners in the abduction of two Americans and a Briton last month. All three were beheaded.

A separate armed group calling itself Al-Islam's Army Brigades, Al-Karar Brigade, said today it had coordinated with officers and soldiers of "the American intelligence" to obtain a "huge amount of the explosives that were in the al-Qaqaa facility."

The claim couldn't be independently verified. The speaker was surrounded by masked, armed men standing in front of a black banner with the group's name on it in the tape obtained by Associated Press Television News.

"We promise God and the Iraqi people that we will use it against the occupation forces and those who cooperate with them in the event of these forces threatening any Iraqi city," the man added.

Nearly 400 tons of conventional explosives have disappeared from the al-Qaqaa facility south of Baghdad, according to the International Atomic Energy Agency.