Opposition leaders in Iran are calling on the country's top clerics to help end the crackdown that followed massive protests of Iran's June 12 elections.

Defeated presidential candidates Mir Hossein Mousavi and Mehdi Karroubi, along with former president Mohammad Khatami, sent a letter to clerics in the holy city of Qom Saturday, comparing the crackdown to the violent methods employed by the former shah before the 1979 Islamic revolution.  

A statement posted by Karroubi on his Internet site went even further, accusing Iranian security agents of using tactics more brutal than those he said were employed by the Israelis against the Palestinians.

Rights groups say hundreds of people were detained during the post-election crackdown.  At least 20 people were reported killed during the protests.

One reformist Web site Saturday said one of the protesters in custody has died.  He was said to be the son of an advisor to another defeated presidential candidate, Mohsen Rezaie.

Mousavi and Karroubi say the June 12 vote was rigged, but Iran's powerful Guardian Council has since upheld the re-election of President Mahmoud Ahmadinejad.

Human rights supporters gathered in about 80 cities around the world Saturday, echoing the calls for Iran's leadership to end the crackdown.

Iranian Nobel Peace Prize winner Shirin Ebadi was expected to speak at one of the rallies in Amsterdam.

Some information for this report was provided by AFP, AP and Reuters.