US troops claimed to have seized the six Iraqis on Thursday, saying they were members of the Mahdi militia of Shia leader Muqtada al-Sadr in Sadr city, northeastern Baghdad.
Earlier on Thursday, US forces appealed to supporters of al-Sadr to hand over their weaponry and withdraw from areas under their control, our correspondent in Karbala reported. US planes dropped leaflets over Karbala with the appeal.
The Iraqi Governing Council (IGC) meanwhile denied that some of its constituent parties were involved in the military operations alongside the US against the residents of Falluja.
Intifad Gambar, spokesman for INC had earlier claimed that four member-groups of the IGC were involved in operations in Falluja.
The IGC also denied Gambar's announcements that lawyer Salim al-Chalabi, the nephew of INC member Ahmad Chalabi, had been named chairman of the special criminal court that is to try deposed Iraqi president Saddam Hussein.
Salim al-Chalabi had not been nominated as the head of the special criminal court but as its administrative director, Aljazeera's correspondent said, quoting the IGC.
In continuing hostage releases, three hostages, two of them Swiss and one Arab carrying Israeli citizenship, were freed on Thursday. The Arab was an employee of the US firm RTI while the Swiss worked for non-governmental organisations.
Meanwhile, a South African security guard working for the US-led occupation force was shot and killed in the Sunni Muslim district of al-Adhamiyah in Baghdad on Thursday.
IGC denies it is involved in
The man was shot dead in a Baghdad shop by an unidentified person dressed in traditional Arab robe and headdress. His Iraqi translator was seriously wounded, police sources and witnesses said.
"A gunman came in and shot them both," Aslan Khalil, a worker at al-Hadba (The Hill) shop where the incident took place, told Reuters Television. "When the gunman came in, he told us: 'This is a Jew, why do you deal with him and sell to him?'"
The owner of the supermarket was also wounded, hit by a bullet in the leg.
Risks to foreigners in Iraq have spiralled this month with the abduction of about 50 foreign civilians.
Most have been released unharmed but at least 26 foreign civilians and private security guards have been killed in violence in March and April, including an Italian killed by kidnappers.
In the flashpoint western town of Falluja, a senior US marine commander warned that unless fighters and residents surrendered their weapons in the next few days, and not weeks, occupation forces could resume their attacks.
The stark warning came two days after implementation began of an agreement under which city leaders called on fighters to hand over their heavy weapons in return for a US pledge to hold back on plans to storm Falluja and allow the return of families that fled the city.
But marines have said that during the past two days, few weapons have been turned in and most the weapons that were surrendered were old or unusable.