Signed by 11 Republicans and two Democrats and dated May 21, the appeal condemns the "ongoing persecution of Iranian political prisoners" since the June vote.
It cites "the hanging of five political prisoners" and reports of detainee torture and asks Clinton to "demand answers for [the] seeming mockery of the judicial process."
"Democratic expression in Iran remains alive despite the repressive steps taken by the government," the letter says, noting student protests that greeted President Mahmud Ahmadinejad's appearance at Tehran University on May 10. "We urge you to vocally support such manifestations of popular will, now and in the coming months as the June 12 anniversary approaches."
-- RFE/RL Central Newsroom