"No power will ever dare to think of launching aggression against Iran. Today, Iran is experienced and powerful," the hardliner said in an address to the nation on the anniversary of the breakout of the Iran-Iraq war in 1980.
"Our armed forces are ready to confront the forces of darkness. If anybody wants to shoot a bullet at us from anywhere, we will cut off his hands."
Ahmadinejad, who was to head later Tuesday to New York to attend the UN General Assembly meeting, demanded that US-led foreign forces leave Iraq and Afghanistan.
"We advise you to go back to your own land. Our region will never accept a lengthy presence of foreigners," the re-elected president, dressed in his trademark light-colour jacket and wearing sunglasses, said in a ceremony attended by top military and administrative officials.
"As you saw in Iraq and Afghanistan, people are against the presence of foreigners. It is impossible (for foreign troops) to have a stable base in the region."
Ahmadinejad's speech was followed by a military parade, an annual event marking the breakout of the war between Iran and Iraq which lasted almost a decade.
A military plane taking part in the parade crashed near Tehran on Tuesday, the official IRNA news agency reported.
"One plane which was conducting manoeuvres during the parade crashed in the village of Vali Abad," near Tehran, the report said. It did not say if there were any casualties.
About a million people died on both the sides in the war which erupted soon after the 1979 Islamic revolution in Iran.
Ahmadinejad said the war, which Iran describes as the "Sacred Defence", was a "humiliation to Satanic forces." Iranian officials refer to the United States as the Great Satan.
"Chemical weapons were used against our nation and the Satanic powers equipped Saddam (Hussein) against our nation. Saddam was backed by certain arrogant powers," the president said, reminiscing about the brutal conflict.
"We ask the arrogant powers to revise their polices… they sell weapons and then talk of peace."
Ahmadinejad's comments come just days ahead of a high-profile international meeting between Iran and representatives of the six world powers on Tehran's latest package of proposals.
The package aims to allay global concerns over Tehran's nuclear programme which Western powers suspect is aimed at making an atomic bomb, a charge vociferously denied by Iran.
Ahead of the talks and his New York visit, Ahmadinejad has once again adopted an aggressive tone, repeatedly blasting arch-foe Israel.
On Friday, at a pro-Palestinian rally, he reiterated his belief that the Holocaust was a "myth", a remark which once again outraged the international community.
During the military parade on Tuesday, in which thousands of Iranian soldiers participated, the military showcased fighter plane, Saegheh, which Iran claims to have built domestically.
The parade took place opposite the mausoleum built for Iran's revolutionary leader Ayatollah Ruhollah Khomeini on the outskirts of Tehran.
