Speaking at a military parade that marked Iran's armed forces' day, Ahmadinejad said the "unrivalled" power of Iranian military secured stability in the Middle East.
Tension with the West has risen in recent months because Iran refuses to scrap sensitive nuclear activities as demanded by the United Nations Security Council. Tehran rejects Western accusations its nuclear work is aimed at making bombs.
"Iran's armed forces are so strong today that the enemies will not even think about violating our territorial integrity," Ahmadinejad said in a low-key speech at the parade.
Israel, widely believed to have the Middle East's only atomic arsenal, has described Iran's nuclear program as a threat to its existence. Although it says it wants a diplomatic solution, Washington has also not ruled out military action.
Troops marched in front of the podium where Ahmadinejad stood with army officers. Some had uniforms in green, white or red — the colors of Iran's flag. Others wore combat gear.
Iran's Shahab 3 missile, which Iranian officials say has a range of about 2,000 km that potentially puts Israel and U.S. bases in the Gulf within reach, was displayed.
Helicopters flew overhead and parachutists landed on the parade area near the tomb of Ayatollah Ruhollah Khomeini, the founder of the Islamic state.
The United States and its European allies are pushing for a fourth round of U.N. sanctions against Iran for its failure to suspend sensitive nuclear work. Washington broke ties with Iran shortly after the 1979 revolution and Tehran reuses to recognize Israel.
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Iran has said it would respond to any attack by targeting U.S. interests in the region and Israel, as well as closing the Strait of Hormuz, a vital route for world oil supplies.
Some experts cast doubt about Iran's military capabilities to deter any attack.
"The Iranian military is capable of creating mischief … but to actually achieve military superiority is highly unlikely," Theodore Karasik, research director at the Institute for Near East and Gulf Military Analysis, told Reuters.
He said Iran's military doctrine was focused on "asymmetric warfare" like using mines and speedboats, to try to disrupt enemy operations.
To cries of "God is Great" Iran showed off its military might, warning potential aggressors that the Islamic state would vigorously repel any attack, state television reported.
Missiles, armored personnel carriers, unmanned surveillance aircraft and small submarines with men wearing aqua-lungs standing next to them were also part of the parade. Some carriers bore banners proclaiming "We will trample America under our feet."
Ahmadinejad urged regional countries to unite to end presence of U.S.-led forces in the Middle East.
"The only way to secure stability and peace in the region is the cooperation and solidarity of the region's governments and nations," Ahmadinejad said. Iran is worried about being surrounded by the armed forces of its archenemy in the region.
"In order to establish regional security, there is absolutely no need for the presence of foreign troops."
The United States has almost 100,000 troops in Iraq but they are largely on bases away from cities. Washington has said it will withdraw all troops by the end of 2011.
(Additional reporting by Fredrik Dahl in Dubai, Writing by Parisa Hafezi, Editing by Matthew Jones)
