Public relations head of the Revolutionary Guards, Commander Seyed Masood Jazayeri, was quoted by the Iranian student news agency ISNA as saying Iran would not initiate a conflict.
However, he said that in retaliation to any attack Iran has proved itself to be "harsh, assertive, hard-hitting and destructive".
"The United States is showing off by threatening to use its wild dog, Israel," he said.
"They will not hesitate to strike Iran if they are capable of it. However, their threats to attack Iran's nuclear facilities cannot be realised. They are aware Tehran's reaction will be so harsh that Israel will be wiped off the face of the earth and US interests will be easily damaged," he warned.
Iran's effort to generate nuclear power is seen by Israel and the US as a cover for nuclear weapons development, allegations that Iran denies.
Meanwhile, US-appointed interim Iraqi Defence Minister Hazim Shaalan warned of invading Iran if it did not stop interfering in his country's internal politics.
"I've seen clear interference in Iraqi issues by Iran," the
minister said in an interview with The Washington Post in Baghdad on Monday.
"Iran interferes in order to kill democracy."
Shaalan accused Iran of taking over some Iraqi border posts and sending spies and saboteurs into Iraq. He said former fighters in Afghanistan had been helped by Iran to get into Iraq.
However, he did not provide evidence supporting his claims.
Muhammad al-Shariati, adviser to Iranian President Muhammad al-Khatami, told Aljazeera that Shaalan's statements were rejected and his government was waiting for "clarification and correction" from the defence minister.
He said Iran sought Iraq's stability and security and any border disputes should be discussed peacefully by both parties.
In apparent reference to The Washington Post, the Iranian adviser also accused "Western media of hyping up" matters in the region.
Iran and Iraq were bitter enemies during the eight-year war they fought in the 1980s.