(CNN) -- A man who appeared on a video shown on an Arabic-language TV network Tuesday is believed to be one of five Britons kidnapped in Baghdad earlier this year, the Canadian-based security firm that employs the man confirmed to CNN.
The video shows a man with a British accent, asking for UK troops to be withdrawn from Iraq.
A spokesman for GardaWorld said company officials believe that the video, which includes a demand for Britain to pull out of Iraq, is authentic.
"We can confirm that we believe this to be a genuine video of one of our employees who has been taken hostage and it is undergoing further analysis," the spokesman said.
Al-Arabiya said the video carries the date of November 18, and that hostage-takers had given Britain 10 days to meet its demand. The video shows two armed militants pointing their machine guns toward the hostage but not to his head. A black banner behind them reads "The Islamic Shiite Resistance of Iraq."
The hostage is heard in English twice on the tape.
He says: "Hi, my name is Jason. Today is the 18th of November." Then he says: "We've been here for 173 days, and I feel we've been forgotten."
The group provided subtitles throughout the video, but the hostage is not heard saying other words because the audio was turned down for those portions.
"I would like to let you know that the kidnappers love the British and the American people but let our army leave Iraq," the subtitles said.
This is the first word on any of the five since the four security guards and a computer expert were seized on May 29 from Iraq's Finance Ministry. They were taken by people posing as security forces and government workers on official business.
The GardaWorld spokesman said the firm, which mainly employs British ex-soldiers, was in contact with the relatives of the hostages. However, he refused to give the name of the man in the video.
He said the situation is "extremely sensitive" and the company is working with British and American security officials in Iraq.
BearingPoint, the employer of another of the men taken hostage, said it "continues to cooperate with the authorities concerning our employee taken hostage in Iraq."
"We cannot comment on the video appearing today in the media. BearingPoint is fully committed to facilitate the safe release of the hostages; they continually remain in our thoughts and prayers," said spokesman Steve Lunceford. BearingPoint is a management and technology consulting firm.
The British Foreign Office said it condemns the airing of the video because it "serves only to add to the distress of the men's families and friends."
"Since day one of the kidnap, consular officials have remained in regular contact with the families of the men," it said. "No matter what the cause, hostage-taking can never be justified. We again call on those holding the men to release them unconditionally."
Al-Arabiya showed the group's statement, which says: "Since the British infidel occupier led by the deposed criminal Blair sent one of his gangs to the Iraqi Ministry of Finance to steal the resources of our people, your mujahedeen brethrens in wounded Iraq arrested that gang and here we show one of its members."
"Blair" is former Prime Minister Tony Blair.
"They have confessed, admitted and announced their true agendas that they came to steal our resources in a deceitful manner where they pretended to be consultants in the Ministry of Finance and we will follow up later with their detailed confessions. Therefore and in the name of the Iraqi people we say to the government of Britain and its queen that one of them used to be employed by them."
The British force, now at about 5,000, is concentrated around the southern city of Basra and is set to be reduced to 2,500 by next spring. But the militants are demanding that all of the forces leave.
"We are only giving you 10 days from the broadcasting of this hostage (message) and we demand that you withdraw all of your forces from our country and to withdraw all the thieves and gangs that you sent to steal our resources and to return what you have stolen already. If you do that, we will release them and if you don't respond to our demands we will kill the hostage on the 10th day as an initial warning and we will follow up with details that you don't want."
U.S. troops in October arrested three people they said were linked to a Shiite insurgent network that is thought to be responsible for the abduction. The U.S. military said the three -- "associated with the Iranian-backed special groups militia" -- were detained in a raids in Sadr City, the densely populated Shiite slum in Iraq's capital. Special groups is the term used by the military to describe Shiite militants that have Iranian backing.
The neighborhood is a bastion of support for anti-American Shiite cleric Muqtada al-Sadr and his Mehdi Army militia, as well as other Shiite militant groups.
The military at the time said the militant network is "known for kidnapping, facilitating the transport of weapons and explosively formed penetrators from Iran to Iraq, as well as bringing militants from Iraq into Iran for military training."
Al-Sadr in August suspended the operations of the militia for about six months after an upsurge of violence between his militia and a rival Shiite force, the Supreme Islamic Council of Iraq's Badr Organization. Al-Sadr and SICI head Abdul Aziz al-Hakim signed an agreement to foster peace and end hostilities among Iraqis.
Despite such developments, authorities believe some Shiite militants who had aligned themselves with the Mehdi Army are not heeding the cease-fire. E-mail to a friend