Family members, lawmakers and other supporters of a former US Marine held in Iran called for his release Monday ahead of his 1,000th day in captivity.

Amir Hekmati was arrested in August 2011, put on trial and found guilty of spying for the CIA. He was subsequently sentenced to death, a penalty that was recently overturned and reduced to 10 years.

"It has been a 1,000 days, it's time for Amir to come home," Hekmati's older sister Sarah said at a vigil just steps from the White House.

Next Monday, Memorial Day in the United States, will mark Hekmati's 1,000th day behind bars, she and other event organizers said.

Her voice breaking as she held back tears, the 33-year-old said Hekmati's father was battling brain cancer and feared not living long enough to see his son again.

Congressman Dan Kildee, who represents Hekmati's home district in Michigan, said he has spoken to President Barack Obama and Secretary of State John Kerry about the case several times.

"It's important that Amir hear our voices, that he know that all of us stand with him," Kildee said.

A fellow Marine veteran, Terry Mahoney, joined the handful of people who turned out for the vigil in hopes of raising awareness about his plight.

"More people need to know about him," he said, sporting a red T-shirt that said "Free Amir."

Hekmati's family insists the dual US-Iranian citizen is not a spy and went to Iran to visit his grandmother.