Iran is using the Lebanese Shi'ite militia Hizbullah as a "proxy" to arm Shi'ite militants in Iraq and Tehran's elite Quds force helped militants carry out a January attack in Karbala in which five Americans were killed, a US general said Monday. The claims were an escalation in US accusations that Iran is fueling Iraq's violence, which Teheran has denied, and were the first time the US military has said Hizbullah has a direct role. A senior Lebanese Hizbullah operative, Ali Mussa Dakdouk, was captured March 20 in southern Iraq, US military spokesman Brig. Gen. Kevin J. Bergner said. Dakdouk was "working in Iraq as a surrogate for the Iranian Quds Force," organizing militants into cells for attacks on US and Iraqi forces, he said. The general also said that Dakdouk was a liaison between the Iranians and a breakaway Shi'ite militant cell led by Qais al-Kazaali, a former spokesman for cleric Muqtada al-Sadr. Bergner said al-Kazaali's group carried out the January attack against a provincial government building in Karbala and that the Iranians assisted in preparations. Al-Khazaali and his brother Leith al-Khazaali were captured with Dakdouk. Dakdouk told US interrogators that the Karbala attackers "could not have conducted this complex operation without the support and direction of the Quds force," Bergner said. Documents captured with al-Khazaali showed that the Quds Force had developed detailed information on the US position at the government building, "regarding our soldiers' activities, shift changes and defenses, and this information was shared with the attackers," Bergner said. The Karbala attack was one of the boldest and most sophisticated against US forces in four years of fighting in Iraq, and US officials at the time suggested Iran may have had a role in it. In the assault, up to a dozen gunmen posed as an American security team, with US military combat fatigues, allowing them to pass checkpoints into the government compound, where they launched the attack. One US soldier was killed in the initial assault, and the militants abducted four others who were later found shot to death. The US military on Monday reported the deaths of five US service members killed in fighting a day earlier, including two soldiers killed in attacks in Baghdad and two soldiers and a Marine who died in fighting in western Anbar province. The deaths brought to 3,582 the number of members of the US military who have died since the beginning of the Iraq war in March 2003. The new accusations against Iran raise tensions between the two countries as Iraq is trying to organize a second round of direct talks between US and Iranian officials in Baghdad. The US-backed, Shi'ite-led Iraqi government, which has close ties to Iran, is pushing the two to ease their disputes to help reduce Iraq's turmoil, but a February meeting between the two sides made little headway. The US military in the past has accused the Quds Force - the external arm of Iran's elite Revolutionary Guards - of arming and financing Iraqi extremists to carry out attacks on US and Iraqi forces. Tehran has denied the US accusations. Bergner said Iraqi extremists were taken to Iran in groups of 20 to 60 for training in three camps "not too far from Tehran." He said that as part of their training, they learned how to build "explosively formed penetrators," a particularly deadly form of roadside bomb that the US has accused Iran of helping militants use. When the militants returned to Iraq, they formed units called "special groups" to carry out attacks, bombings and kidnappings. "Our intelligence reveals that the senior leadership in Iran is aware of this activity," he said. Asked if Iran's supreme leader Ayatollah Ali Khamenei could be unaware of the activity, Bergner said, "That would be hard to imagine." Hizbullah spokesmen in Lebanon said they were checking into the claims Dakdouk was a member of their group and would not comment. The group has in the past denied any activities in Iraq. In late 2005, British Prime Minister Tony Blair said his government suspected that Iran and Lebanon's Hizbullah might be supplying technology and explosives to Shi'ite Muslim militant groups operating in Iraq, but he provided no proof. Dakdouk, a 24-year veteran of Hizbullah, was "tasked to organize the special groups in ways that mirrored how Hizbullah was organized in Lebanon," the general said. Dakdouk was ordered by Hizbullah's leadership to work with the Quds Force and went to Iran in May 2006 to meet with Quds Force commanders, Bergner said. He then made four trips to Iraq over the next year. Hizbullah, he said, helps the Iranians as a "proxy ... to do things they didn't want to have to do themselves in terms of interacting with special groups," Bergner said. The military was still investigating how large a presence Hizbullah has in Iraq, but he added that the group was present "not as a network." Dakdouk was captured with documents instructing the special groups on techniques, including how to attack a convoy, and with a personal diary detailing meetings with Iraqi militants. Al-Khazaali also had documents with details on 11 separate attacks on US force, Bergner said. A total of 18 "higher-level operatives" from the Iranian-backed special groups have been arrested and three others killed since February, Bergner said.