An official from the Russian energy service company, Interenergoservice, told Aljazeera on Monday two Iraqi company guards might have been killed during the confrontation with the armed captors.
A Russian engineer in Iraq told Aljazeera the 11 worked at power plants.
Meanwhile, seven Chinese hostages captured in Iraq have been released, the official Xinhua news agency has reported.
The Chinese have been reported missing. They entered Iraq from Jordan early on Sunday and were abducted in Falluja, the Iraqi foreign ministry and a Chinese diplomat in Baghdad said on Monday.
China News Service identified the hostages as Xue Yougui, Lin
Jingbing, Lin Kongming, Li Guiwu, Li Guibing, Wei Weilong and Chen Xiaojin. The oldest is 49, the youngest 18.
The agency quoted a Chinese businessman in the city as saying the seven were being looked after by the Association of Muslim Scholars, the highest Sunni authority in Iraq.
The men were from eastern Fujian province, which has a long tradition of being the source of illegal immigrants travelling overseas in search of work.
Chinese security sources in Fujian told Aljazeera the hostages went to Iraq on their own responsibility. "No Chinese organisation or company has sent them to Iraq," the sources added.
Earlier on Monday, the Chinese ambassador in Baghdad, Sun Bigan, in an interview with Aljazeera, called on the captors to release the hostages.
"I seize this opportunity to call on the captors whatever they are to consider the friendship and links between the two countries and to release the hostages so they can return to their families".
"It is known that Chinese people have good friendly relations with the Iraqi people and there is no flaw or tension in our relations"
Chinese ambassador to Baghdad
"It is known that Chinese people have good friendly relations with the Iraqi people and there is no flaw or tension in our relations," added the ambassador.
"The hostages came to your country for trade and ordinary transactions and they have done nothing to infuriate the Iraqi people or ruin the relationship between the two countries."
Also on Monday, it was reported that seven US contractors working for a Halliburton subsidiary have gone missing in Iraq after an attack by Iraqi resistance fighters on their convoy near Baghdad international airport.
Lieutenant General Ricardo Sanchez, the head of US occupation force in the country, on Monday told reporters in Washington from Baghdad the seven contractors worked for Kellog, Brown and Root.
Two US soldiers were also missing after the attack on Friday.
Released captives were lorry
drivers supplying troops
Meanwhile, two Czech state television journalists and one radio correspondent are missing in Iraq and may have been kidnapped, the public broadcasters said on Monday.
Martin Krafl, spokesman for Czech Television, said a cameraman, Petr Klima, and a reporter, Martin Kubal, had hired a car and driver to take them from Baghdad to neighbouring Jordan on Sunday morning.
Krafl said the two were last seen on Sunday morning, but gave no further details other than to say that all contact had been lost with the them.
"I can confirm that we have lost contact with them," Krafl
said of the television journalists. He could not confirm reports
the two were kidnapped, but added that this was a possibility.
In addition, state radio reporter Vit Pohanka who was also
due to make a trip from Baghdad to Amman, is unaccounted for, the local CTK news agency said, quoting Czech Radio's Foreign Editor Jiri Hosek.
On Sunday, a British contractor and eight others held by Iraqi kidnappers were freed, but the fate of three Japanese and an American captive remained unclear.
A videotape aired by Aljazeera TV on Sunday showed the frightened captives holding their passports and giving their nationalities. The hostages were seen guarded by masked men with arms.
The hostages were three Pakistanis, two Turks, an Indian, a Nepali and a Filipino.
The Iraqi group said the hostages were drivers of lorries used for transporting supplies to occupation troops in Iraq.
"We have released them in response to a call from the Association of Muslim Scholars ... after we were sure that they will not deal with the occupation forces again," the group said in the tape.
Meanwhile, uncertainty still surrounds the fate of the Japanese hostages, with their captors threatening to kill them unless Japan withdraws its forces.
Families of Japanese captives
have pleaded for their release
Aljazeera also received a letter from the families of the Japanese hostages, pleading for information and backing their captors' demand for Tokyo to pull its troops out of the war-ravaged country.
Also on Sunday, Aljazeera TV aired a tape showing the bodies of two men reported to be US intelligence officers killed in Falluja. A voice on the tape said the two Americans were CIA officers working in Iraq.
The tape showed the bloodied bodies of two foreign men lying on the ground, one shot in the back and another in the leg, surrounded by several Iraqi men. It was not clear when the footage was filmed, or by whom.