Iran and the United States are also at loggerheads over a nuclear programme that Washington says is to make bombs. Tehran denies this.
The United States has said that it favours diplomacy to resolve the standoff, but has not ruled out military action.
Asked about Moussa's comments, Sean McCormack, the US state department spokesman, reiterated that all options remained on the table but he said the United States was working in a "co-operative fashion" with its allies in the Gulf over Iran.
"The president has always said 'You never take any option off the table', but I think we're being quite transparent in the ways that we're seeking to deal with the various threats posed by Iran, really to the region," McCormack said.
Moussa did not say how he assessed the likelihood of a US attack.Israeli response
Israel has also threatened to respond to Iran's nuclear ambitions "with all the means at our disposal".
On Wednesday, Ehud Olmert, the Israeli prime minister, told a security conference that the international community had no choice but to act forcefully against Iran and its president, Mahmoud Ahmadinejad, who has called for Israel's destruction.
|"As serious as the Iranian threat is, the threat of nuclear attack on Israel is by no means imminent."|
Israeli prime minister
"When the leader of a country announces, officially and publicly, his country's intention to wipe off the map another country, and creates those tools which will allow them to realise their stated threat, no nation has the right to even to weigh its position. It is the obligation of every country to act against this with all its might," Olmert said.
Olmert said Israel supports using diplomacy and that there is still time for international pressure to work.
"As serious as the Iranian threat is, the threat of nuclear attack on Israel is by no means imminent," he said.
Israeli authorities have been vague about whether they'd be willing to carry out military strikes against Iran, though they have not ruled them out.
Asked about Bush's remark on Shia fighters, Moussa said: "I would agree that any kind of extremism, in thoughts or in policies or harsh conservatives, any kind are very dangerous."
But he stopped short of blaming Iran. "It would not be appropriate" to say whether Iran is responsible for destabilising Iraq through support of fighters, he said.
Moussa said the United States needed to move from use of military force towards dialogue, to resolve the violence in Iraq and to reduce US-Iranian tensions.
He said that he supported proposals for talks with Iran and Syria.
"If there were to be a war, other genies will get out of the bottle," he said. "You cannot imagine the impact on the Gulf countries, on the Mediterranean."