Former Iranian President Mahmoud Ahmadinejad (above) sent a letter on Sunday to Donald Trump | Spencer Platt/Getty Images Mahmoud Ahmadinejad’s Dear Donald “Four years is a long period, but it ends quickly,” wrote the former Iranian president to Trump.

Iran’s former President Mahmoud Ahmadinejad on Sunday sent a 3,500-word letter to Donald Trump, offering advice and striking a surprisingly conciliatory tone, given the recent tensions between Tehran and the new American leader.

Ahmadinejad, a hardliner who left office in 2013, praised Trump's winning election camapign last year as having "truthfully described the U.S. political system and electoral structure as corrupt," according to a copy of the letter published by Iranian media and reported on by the Associated Press.

The former Iranian leader gave the letter to the Swiss embassy in Tehran, which represent U.S. interests.

"Four years is a long period, but it ends quickly," he wrote by way of advice. "The opportunity needs to be valued, and all its moments need to be used in the best way."

In the letter, Ahmadinejad decried U.S. "dominance" over the United Nations, as well as American meddling in the world that has brought "insecurity, war, division, killing and (the) displacement of nations," according to AP.

In the wake of Trump's order to ban travel to the U.S. by citizens from seven majority-Muslim nations, including Iran, that was blocked by American courts, Ahmadinejad urged the new president to "value respect toward the diversity of nations and races."

Ahmadinejad didn't mention Iran's nuclear program, which has been at the center of the country's disputes with the U.S. this century.