Former boxing champion Muhammad Ali wants Iran to free two American hikers held in Iran since 2009.
Josh Fattal and Shane Bauer crossed the Iranian border by mistake, according to their families, but the Iranian government claims the men are spies. A third hiker, Sarah Shourd, was captured with them, but was released on bail in September.
In a letter, Ali asks Iran's supreme commander Ayatollah Ali Khamenei to free the men as a brother in Islam.
"Please show the world the compassion I know you have in your heart," Ali said in the letter.
The 69-year-old also wrote to Khamenei last year shortly before Shourd was released.
Ali founded a center for world peace in Louisville, Ky. He is also one of the most well-known U.S. Muslims.
Ali traveled to Iran in the early 1990s when he tried to secure freedom for prisoners during the Iraq-Iran war.
The boxing legend said he would be willing to go again if his health allows it.