"The Americans must understand that if they make a surprise attack on Iran, their interests around the world will be under retaliation, our country will give them diploid reply," Khamenei was cited as saying.

The supreme leader stressed that the U.S. has been threatening Iran for many years, but the Islamic republic would not be really concerned about it.

Earlier on Wednesday, Iran's hardline President Mahmoud Ahmadinejad vowed that the country would neglect the UN calls to freeze its sensitive nuclear activities.

"We won't retreat from our legal rights," Ahmadinejad was quoted as saying by the official IRNA news agency.

"If the international institutions acknowledge our country's rights, we will also respect their demands, but if they deprive our legal rights, I don't think Iran could accept any requests," he said.

"If they can carry out their responsibilities legally, there's no reason for us to reconsider our relations with them," the president stressed.

The two leaders made the flinty remarks just two days before a nuclear deadline set by the UN Security Council expires, which demanded Iran to suspend all uranium enrichment activities by Friday.

Based on a Feb. 4 resolution, the International Atomic Energy Agency (IAEA) on March 8 handed over the Iranian nuclear issue to the UN Security Council.

After weeks of heated bargains, the 15-member Security Council on March 29 approved a non-binding presidential statement, asking Iran to suspend uranium enrichment activities in 30 days and demanding the UN nuclear watchdog to report on Tehran's compliance.

Mohamed ElBaradei, chief of the IAEA, is expected to submit the report to the Security Council in the coming days.

With the deadline looming, President Ahmadinejad said on Monday that he believed sanctions were unlikely, vowing to press ahead with the nuclear program.

He also warned that Tehran would "reconsider" its cooperation with the IAEA, hinting a possible withdrawal from the nuclear Non-Proliferation Treaty, if western countries continued to prevent Iran from obtaining peaceful nuclear technologies.

Earlier this month, Iran officially declared that it had gained ticket to joining the global nuclear club by having produced 3.5 percent enriched uranium, a technological leap in the process for nuclear power plant construction, which immediately aroused strong international concern.

The United States has accused Iran of secretly developing nuclear weapons under a civilian front, but Iran dismissed the charge, saying that its nuclear program is fully peaceful.