REPORTING FROM TEHRAN -- Iran will strike back with equal force if the United States or Israel attacks it over its nuclear program, Ayatollah Ali Khamenei warned in an address from the eastern city of Mashhad in observance of Nowruz, the Persian new year.

"The holy Koran states that if an enemy attacks you first, the enemy will certainly be defeated," he said. “This is divine law. We are not thinking of attacks and aggression, but we are attached to the existence and identity of the Islamic republic."

Khamenei urged the U.S. to have a respectful attitude toward Iran. His words followed a video address from President Obama to Iranians, the fourth annual address he has created for Nowruz.

Obama said there was no reason for Iran and the U.S. to be opposed, but criticized Internet censorship as an "electronic curtain" to repress information. Iran has stepped up its efforts to control the Web this year, including tighter rules for Internet cafes and a new council to oversee the Internet.

"Suppressing ideas never succeeds in making them go away," Obama said.

It is unclear how many Iranians saw Obama's message in light of the Internet restrictions; it may have reached Iranians who use illegal satellite dishes to pick up Farsi broadcasts of Western channels.

Iran and the United States have been at odds over its nuclear program, which Iran argues is solely for peaceful purposes. Khamenei has said that owning nuclear weapons is a sin. Though U.S. intelligence agencies do not believe Iran is actively trying to build an atomic bomb, officials believe it is pursuing research that could make it capable of creating a weapon in the future.

Tehran has offered to resume negotiations. Obama has said that he favors diplomacy, not military strikes, to resolve the dispute, but recently warned that time may be running out for talks.

The Iranian supreme leader traditionally makes two televised speeches to mark the new year, including one from Mashhad, where he grew up and became known as an activist before the Islamic Revolution in 1979.

Besides the stern words to Israel and the U.S., Khamenei also hailed the last year as a success for Iran and dedicated the new year to "Iranian labor and investment."