U.S. diplomats used a meeting with their Iranian counterparts to press for the release of Americans being detained in Iran, the Trump administration said Thursday, according to The Associated Press.

It is the first public acknowledgment of direct U.S.-Iranian discussions since President Donald Trump took office.

State Department spokesman Mark Toner said the talks occurred on the sidelines of a meeting in Vienna this week that focused on implementation of the Iran nuclear deal.

Although Trump and his top advisers have publicly criticized Iran for its support of Syrian President Bashar Al-Assad, Yemeni rebels and other jihadist groups throughout the Middle East, American officials haven't spoken about any continuation of U.S.-Iranian conversations that became routine under the Obama administration.

At Tuesday's meeting in Austria, Toner said, "the U.S. delegation raised with the Iranian delegation its serious concerns regarding the cases of U.S. citizens detained and missing in Iran, and called on Iran to immediately release these U.S. citizens so they can be reunited with their families."

Toner cited the detentions of Iranian-American businessman Siamak Namazi and his 81-year-old father, Baquer Namazi, who are serving 10-year prison sentences for "cooperating with the hostile American government." The younger Namazi has been detained since October 2015 and his father was taken into custody in February 2016.

Toner also noted it has been more than a decade since the disappearance of Jewish-American former FBI agent Robert Levinson.

Levinson, a father of seven from Coral Springs, Florida, vanished during a trip to Iran in 2007, disappearing on Kish Island off Iran's coast.

He was not included in a last year’s breakthrough prisoner swap between Iran and the U.S., which saw four American citizens freed in return for the release of seven Iranians jailed in the United States.

The Trump administration has previously promised to bring Levinson back to the United States.

The only photos and video of Levinson emerged in 2010 and 2011. He appeared gaunt and bearded with long hair, and was wearing an orange jumpsuit similar to those worn by detainees at the U.S. prison at Guantanamo Bay, noted AP.

"Iran committed to cooperating with the United States in bringing Bob home and we call on Iran to fulfill this commitment," Toner said on Thursday, adding, "The United States remains unwavering in its efforts to return Bob to his family."

Levinson's family in March filed a lawsuit against the Iranian government in the United States.

The lawsuit seeks unspecified damages from Iran, in part for inflicting emotional distress on Levinson’s wife and seven children.