“My heart aches for him. … I just want to see him home safe and sound,” Joanne White said by phone.

News about Michael White’s detention comes amid rising tensions between the United States and Iran. Those strains have particularly increased since May, when the United States withdrew from a nuclear deal with the Islamic republic and reinstated sanctions against it.

CNN has sought comment from the governments of Iran and Switzerland, which represents the United States’ diplomatic interests in Iran.

A US State Department representative said the department was “aware of reports of the detention of a US citizen in Iran,” and that the department has “no higher priority than the safety and security of US citizens abroad.”

“Due to privacy considerations, we have no additional information to provide at this time,” the representative said.

Michael White flew from Los Angeles to Dubai on July 9, and then on to Iran, his mother said.

He was visiting a woman whom he said was his girlfriend, she said. He met her online about four or five years ago, and he had visited her four times over the last few years, Joanne White said.

Michael White’s wife, Lupe White, said she last saw her husband July 9 and he texted her a day later saying he was on a business trip for two weeks. Lupe White said he has had an online relationship with a woman in Iran for six years and would go see her for two weeks at a time.

She and her husband, who have been married for almost 15 years, have discussed divorce, she said, but she was hoping they had strengthened their relationship in the past six months as she helped him through his chemotherapy.

“I still love him. He is my partner. He is still my husband,” she said.

She said she had not been contacted by the US State Department and was unaware he was in prison until being contacted by CNN. White said she talked to police at her home after she called them when he did not return home.

Other foreign nationals held in Iran

White would be one of several US citizens and other foreign nationals held in Iran. The State Department advises Americans not to travel to Iran, “due to the risk of arbitrary arrest and detention of US citizens.”

Detained Americans in Iran include:

• Siamak Namazi, and his father, Baquer Namazi, Iranian-Americans who have been detained since October 2015 and February 2016, respectively. The son was detained while visiting relatives in Tehran; both were sentenced in 2016 to 10 years in prison for what the Iranian government said was “cooperating with Iran’s enemies,” a euphemism that usually implies cooperating with the United States. American officials have demanded their release, saying the father and son did nothing wrong and do not deserve imprisonment.

• Xiyue Wang, a Chinese-born US citizen and Princeton University graduate student, was detained in August 2016 while doing scholarly research and studying Farsi, the university said. The Iranian government in 2017 said Wang was sentenced to 10 years in prison after being convicted of spying. US officials have demanded his release.

US officials have also pushed Iran for information about the whereabouts of Robert Levinson, a former FBI agent and CIA contractor who went missing in Iran in 2007. Iran has denied having anything to do with his disappearance and said it doesn’t know where he is. His family sued Iran over his disappearance in 2017.

In December, six families of foreign or dual nationals held or believed to have disappeared in Iran — including the families of the Namazis and Levinson — issued an open letter, along with the New York-based Center for Human Rights, alleging they essentially were political hostages detained without due process.

Recent releases

Iran has released Americans and other foreign nationals in recent years.

In January 2016, Iran freed four US prisoners — Washington Post journalist Jason Rezaian, Marine veteran Amir Hekmati, Christian pastor Saeed Abedin, and Nosratollah Khosravi-Roodsari — in exchange for the US granting clemency to seven Iranians indicted or imprisoned in the United States.

A fifth American, Matthew Trevithick, was separately released that month, US officials said.

Those releases came months after the international deal to restrict Iran’s nuclear program — the same deal from which the US withdrew last year.

In December, Abbas Edalat, a British-Iranian professor who was detained in Iran for eight months after being accused of affiliations with an anti-Iran group, was allowed to return to the United Kingdom.