Iran's Supreme Leader Ayatollah Ali Khamenei on January 9, 2018 gesturing during a rally in the capital Tehran Image Credit: AFP

Iran's Foreign Ministry confirmed Wednesday that it has detained a U.S. Navy veteran who was arrested last summer when he went to the country to visit his girlfriend.

Foreign Ministry spokesman Bahram Ghasemi made Iran's first acknowledgment that it is holding Michael White, 46, of San Diego, according to a report in the semiofficial Tasnim news agency.

"An American citizen was arrested in the city of Mashhad some time ago, and his case was conveyed to the U.S. administration on first days," he said.

White's arrest was first reported by IranWire, an online venture focusing on Iran news reported by the Iranian diaspora. It interviewed a released Iranian prisoner who said he had met White at Vakliabad Prison in Mashhad this fall. It remains unclear what, if any, charges have been brought against him.

Secretary of State Mike Pompeo, who is in the Middle East on a tour designed to bring more pressure on Iran, declined Wednesday to discuss White's arrest.

At a stop in Jordan on Tuesday, Pompeo said the United States would ramp its efforts to counter Iran's influence in the region, "redoubling not only our diplomatic but our commercial efforts to put real pressure on Iran."

White's arrest only adds to the tension that has existed between Iran and the United States since the Trump administration withdrew from the 2015 nuclear deal and reimposed sanctions that had been lifted under the agreement.

White is at least the fourth U.S. citizen being held in Iran on accusations of espionage. In the past, Iran has agreed to prisoner swaps, releasing some U.S. prisoners as Iranian prisoners in U.S. cells were freed. The last such exchange took place when the nuclear agreement took effect in early 2016.

Iranian-American businessman Siamak Namazi was arrested in 2015, and his father, Baquer, also was arrested a few months later when he went to Tehran to try to secure his son's release.

Princeton scholar Xiyue Wang has been imprisoned in Iran for more than two years since he was arrested on suspicions arising from the historical research he was doing. And Robert Levinson, a retired FBI agent, has not been heard of since he disappeared in 2007 while on a visit to Kish Island.

It is unclear why it has taken so long for word to get out about White's circumstances since he was arrested in late July. His mother told the New York Times she learned he was alive and in prison just three weeks ago.