US State Department spokesman Adam Ereli said Iran's concerns that it was threatened by the troops were "unwarranted."
"The United States forces are there as part of a multinational force, at the invitation of the ... the sovereign authority of Iraq, the interim Iraqi government, pursuant to UN Security Council resolutions, to help support the stability and security of Iraq," Ereli said.
"So there's no cause for seeing them as threatening," he said.
"Iraq's neighbors have an interest in joining with all of us working in Iraq to ensure that those who are trying to unsettle, destabilize or otherwise work against the government of Iraq are defeated," Ereli added.
Iran's defence minister, Rear-Admiral Ali Shamkhani, on Wednesday warned the United States and its ally Israel against launching strikes against Iran's nuclear facilities.
"Some military commanders in Iran are convinced that preventive operations which the Americans talk about are not their monopoly," he told Qatar-based Al-Jazeera television, adding that "the US military presence (in Iraq) will not become an element of strength (for Washington) at our expense."
Ereli sought to appease what he called Tehran's "rhetoric concerning strikes and counterstrikes over Iran's nuclear program."
The United States accuses Iran of using its civilian atomic energy program as a cover for the secret development of nuclear weapons and has led a charge at the International Atomic Energy Agency (IAEA) to press Tehran into admitting it and abandoning the aim.
"From the United States point of view, this is a program that is of serious concern and it is something that we are committed to pursuing through diplomatic means, as evidenced by our active diplomacy through the International Atomic Energy Agency," Ereli said.
White House spokesman Scott McClellan said: "What the Iranian governement needs to do is to end its pursuit of nuclear weapons. This is what our priority is when it comes to Iran and we made it very clear.
"Germany, France and the British are making it very clear to the Iranians as well," McClellan said. "They need to fully comply with their international obligations and abide by what they say they would do."