Iran said on Wednesday it would harm US interests anywhere in the world if the United States launches an attack on the Islamic Republic, which is embroiled in a nuclear standoff with the West.
The comments by Supreme Leader Ayatollah Ali Khamenei, reported by state television, come two days before the UN nuclear watchdog is due to report on whether Iran is complying with UN demands to halt uranium enrichment. Tehran says it will not stop.
The United States, which accuses Iran of trying to build atomic bombs, has said it wants a diplomatic solution to the dispute but has not ruled out a military option if diplomacy fails.
"The Americans should know that if they assault Iran their interests will be harmed anywhere in the world that is possible," Khamenei was quoted as saying by a television announcer.
"The Iranian nation will respond to any blow with double the intensity," he added.
The United States has been pushing to impose sanctions if, as Washington expects, Iran is found in the report by the International Atomic Energy Agency to have flouted UN demands.
Fellow UN Security Council members Britain and France have supported such a step, but sanctions are opposed by Russia and China, which like the other three permanent members of the council have the power to veto council resolutions.
Iran said on Tuesday it would suspend its relations with the IAEA if sanctions were imposed. Diplomats said this could mean withdrawing from the nuclear Non-Proliferation Treaty (NPT).
President Mahmoud Ahmadinejad on Wednesday reiterated his view that Iran could reconsider its commitment to the NPT and its cooperation with the IAEA if it felt it was not benefiting from abiding by international protocols.
"We have asked them (the UN watchdog), and we are waiting for an answer: what have they given us in reward for doing our duty? What sort of help have they given us?" he told reporters after meeting Sudan's president in Tehran.
"We hope they fulfil their duties and make it unnecessary for the Islamic Republic of Iran to reconsider its relations with them," he said.
Although Iran says it bases its nuclear policy on the NPT, it has already pulled out of the treaty's Additional Protocol, which allows snap inspections of atomic facilities. It took that step after Iran's atomic file was referred to the Security Council.
Iran often grumbles that it does not benefit from the NPT's entitlement to shared technology.
But Western diplomats argue Iran's demand for shared know-how under the NPT is spurious as this entitlement would only be valid if it were certain that Tehran's ambitions were peaceful.
The IAEA has said that after three years of investigation it still cannot confirm that Iran does not have a military programme, as Tehran insists, but has found no hard proof.
"They should know that they cannot impose any decisions upon us by using the name of the IAEA and UN Security Council because illegal decisions do not become legitimate just by using the name of the agency and Security Council," Ahmadinejad said.
"Our scientists have mastered this technology with their own brains, their own might and their own hands," he said.
Despite insisting the atomic programme is home-grown, Iran has been heavily reliant on Russian expertise and on black-market trade linked to the father of Pakistan's nuclear bomb Abdul Qadeer Khan.