"Iran has the highest level of defense-military preparedness to confront any type of threat and excessive demands," Defence Minister Amir Hatami was quoted as saying by the Islamic Republic News Agency (IRNA).
He said Iran would defeat an American and Israeli alliance.
The United States has sent further military forces to the Middle East, including an aircraft carrier, B-52 bombers and Patriot missiles, in a show of force against what U.S. officials say are Iranian threats to its troops and interests in the region.
The commander of Iran's elite Revolutionary Guards said: "We are on the cusp of a full-scale confrontation with the enemy," the Fars news agency reported.
Major General Hossein Salami, named head of the force last month, added: "This moment in history, because the enemy has stepped into the field of confrontation with us with all the possible capacity, is the most decisive moment of the Islamic revolution."
Separately on Wednesday, a senior Iranian official told Reuters that Tehran was ready for all scenarios from "confrontation to diplomacy" but the United States could not afford another war in the Middle East.
Washington ordered the departure of non-emergency government employees from Iraq on Wednesday after repeated U.S. expressions of concern about danger posed by Iranian-backed forces.
Israel will stand with the United States to confront Iran, Israeli Prime Minister Benjamin Netanyahu said on Tuesday.
"We are united in our desire to stop Iranian aggression," he said. "Israel and all the countries of the region and all the countries who seek peace in the world should stand together with the United States against Iranian aggression."