US Secretary of State Condoleezza Rice chided Iran for trying to act "tough" after it fired a new long-range missile for the first time, but warned Tehran would "suffer greatly" if it used the weapon in anger.
Iranian forces launched the Shahab-3 ballistic missile on Wednesday as they began 10 days of war games that coincide with US-led efforts to impose UN-mandated sanctions on Iran over its nuclear programme.
"I think they're trying to demonstrate that they're tough," Rice said of the missile test.
"But the Iranians also I think are not unaware that the security environment is one in which if they actually were to do something, Iran would suffer greatly and so I think they probably understand that," she said in a radio interview.
Referring to Iran's refusal to comply with a UN Security Council resolution demanding it abandon suspect nuclear activities, Rice said, "I think the Iranians are a threat and that's why the international community's got to be strong in resisting their ambitions."
She said on Wednesday's missile test was Iran's way of telling the world "you're not going to keep us from getting a nuclear weapon... The world has to say to them, yes, we will."
Rice was speaking amid ongoing negotiations between the US and its big power partners over a package of sanctions designed to force Iran to give up its uranium enrichment programme.
Iran insists the programme is aimed at providing fuel for nuclear power plants while Washington and others suspect the ultimate aim is to develop atomic weapons.