Phoenix —The mother of a U.S. Navy veteran detained in Iran is calling for his immediate release. Michael White, 46, has been in an Iranian prison for more than six months.

Joanne White said she prays every day that her son Michael will be freed from prison in Iran before it's too late. She worries his recurring cancer could come back and he could die.

White said the Navy veteran was on his third trip to Iran last July. Though he was married, he was visiting his girlfriend he had met online, when he disappeared.

"I knew he wasn't dead. I felt that in my heart. But I didn't think he was OK," she said.

Nearly five months later, she learned he was in prison in the northeastern Iranian city of Mashhad. But she hasn't gotten any phone calls from her son.

An Iranian judicial official said last week White is being sued by a private plaintiff, referring to a complaint by a citizen, not the government. The official did not rule out possible "security-related charges."

Iran has incarcerated other Americans on charges of espionage, which they have denied.

"No, he's not a spy, not at all," White said.

She wants the U.S. to negotiate with Iran for her son's release. Secretary of State Mike Pompeo told CBS News' "Face the Nation" the U.S. is using "every tool" in its arsenal to free Americans detained all over the world.

Asked by CBS News specifically what the White House was doing to try and secure White's release, a senior administration official said the government was in, "regular contact with the families of Americans who are detained abroad. However, due to privacy reasons, we are not able to provide details on Mr. White's case. We also cannot provide any detail of our private diplomatic discussions or internal policy deliberations with Iran."

"I think my son's life is worth a lot. It's worth a lot to me," White said. "I love him and I'm praying for him. That's what I'd tell him. And stay strong, please stay strong."