Iraqi officials expressed concern on Sunday that more than 100 American soldiers in Iraq may be infected with swine flu, fearing they could spread the disease in the country. Also on Sunday, Iraq's foreign minister said he was hopeful that Iran would release three Americans arrested after they had apparently strayed into Iranian territory on a hiking trip. And two Western contractors working for a British security company were killed, authorities said, by a colleague who also worked for that company, ArmorGroup Iraq. The U.S. military said on Sunday that swine flu had been diagnosed in 51 American troops in Iraq, while another 71 soldiers were suspected of carrying the virus, The Associated Press reported. Members of parliament have expressed alarm that U.S. troops could be vectors for introducing the disease into Iraq, particularly among the Iraqi military with whom they patrol. Ever since the virus began to spread, Iraqi officials have been greeting visitors to the country with health teams, who take the temperatures of passengers as they disembark from airplanes. So far seven foreign visitors have been registered as having swine flu since the screening started, said Dr. Ihsan Jafar, director general of communicable disease in Iraq's Ministry of Health. U.S. soldiers, however, are not subject to screening by Iraqi officials. 'We expect more cases among American soldiers,' Jafar said. He warned against overreaction. 'A big increase in a short time would be very dangerous,' he said, 'but until now we don't have that.' Bassim Sharif, spokesman for the Health and Environment Committee in parliament, said that U.S. soldiers were 'coming from America without any screening.' In addition, the policy of allowing every U.S. service member an approximately two-week break back home increases the possibility that they would introduce swine flu. 'We have been afraid of this,' he said. 'They are in contact with Iraqi soldiers within the bases, or in the joint patrols.' The U.S. military says that it conducts its own screening of service members before they enter Iraq and that those suspected of carrying swine flu are put in isolation, the AP reported. The United States has previously said it would report any cases of the virus to the Iraqi government under an agreement between the countries. The foreign minister, Hoshyar Zebari, said Sunday that he was hopeful that three Americans arrested for crossing into Iran would be released soon. 'I've heard they decided to release them on our intervention,' he said in a telephone interview. 'But really I don't have any confirmation.' Zebari said he met last Thursday with Iran's ambassador, Hassan Kazemi-Qomi, to request the release and to confirm the status of the three. 'He did confirm to me that they have been detained for allegedly entering the country, and they are being interviewed by the Iranian authorities,' Zebari said. 'For humanitarian reasons we decided on our own initiative that we wanted to raise the issue with them,' he said. He indicated that the request was not made at the behest of the United States. The three -- Shane Michael Bauer, a freelance journalist; his girlfriend, Sarah Emily Shourd; and a friend, Joshua Felix Fattal -- had apparently strayed across the border on July 31 while hiking in the Ahmed Awa resort area in Kurdistan. The U.S. government has asked the Swiss Embassy in Tehran, which represents American interests in the country, to ascertain the fate of the three. Iraq has close relations with Iran even as it depends heavily on the United States for military support. Zebari said the ambassador was receptive to his request and he was therefore hopeful of a release. Some hard-liners in Iran have accused the Americans of being spies. The ambassador was not immediately available for comment. In another development, two contractors for a British security firm were shot dead in a fight on Sunday with at least one other employee of their company in Baghdad's heavily guarded Green Zone, according to Maj. Gen. Abdul Karim Khalaf, a spokesman for the Ministry of the Interior. The victims and the person accused of killing them all worked for ArmorGroup Iraq, Khalaf said. The dead were identified by ArmorGroup's parent company in the Britain, G4S Risk Management, as Paul McGuigan, a Briton, and Darren Hoare, an Australian. Patrick Toyne-Sewell, a spokesman for G4S in London, said, 'We are working closely with the Iraqi authorities to investigate the circumstances of their deaths.' Khalaf said that Iraqi police officers responded when they heard gunfire around dawn on Sunday and arrested a British employee of the company as a suspect in the shooting deaths. He said he could give no more details pending further investigation by Iraqi authorities. An official close to the investigation, speaking on condition of anonymity because the investigation is not completed, identified the suspect as Daniel Fitzsimons. The official described Fitzsimons as an experienced security 'operator' who has worked for ArmorGroup and other security firms in Baghdad since 2004 and had only recently been rehired by ArmorGroup. A second British employee of the company was reported to have been taken into custody only as a witness and was later released. An Iraqi employee of the company was wounded in the shooting, Khalaf said. He said the men were fighting inside a trailer used to house staff members on the ArmorGroup's premises. ArmorGroup provides armed escorts and other security services in Iraq. It was one of the Western security companies that lost their immunity from prosecution by the Iraqis on Jan. 1, when a new Status of Forces Agreement between Iraq and the United States took effect. Iraqis had lobbied hard for lifting the immunity because of a series of shootings in which Iraqi civilians were killed by Western security firms, most notoriously one in which guards working for Blackwater Worldwide killed 17 bystanders in Baghdad. Several of the company's employees went on trial in the United States. The shooting on Sunday was the second episode of a violent killing among foreign security contractors in the Green Zone recently. On May 22, James Owen Kitterman was found stabbed to death in his car. Five American security contractors were arrested by Iraqi authorities but later released; no charges have been brought in that case. Khalaf said there was no connection between the two cases. 