WASHINGTON (CNN) -- The State Department called on Iran on Friday to pony up any information it has on a former FBI agent who vanished there last year.
Christine Levinson, wife of Robert Levinson, went to Tehran last year to try to learn her husband's fate.
State Department spokesman Sean McCormack urged Tehran to share "any and all information" about Robert Levinson, who disappeared from Iran's Kish Island over 19 months ago.
"The U.S. Department of State remains committed to determining Mr. Levinson's whereabouts, and returning him safely to his family that includes seven children, one grandchild and a second grandchild on the way," McCormack said in a statement.
Senior administration officials say the United States is increasing pressure on Iran to provide information on Levinson's whereabouts. Several officials have said they suspect Iranian authorities are holding Levinson in a jail inside the country.
However, they stress they have no information confirming their suspicions and have consistently voiced frustration with the lack of developments in the case.
"Some people suspect he is being held by the Iranian government, but nobody knows that for a fact, or we would be saying that," one senior State Department official said. "We all agree the Iranians are not putting forth 110 percent effort to find this man."
Levinson is a retired FBI agent from Coral Springs, Florida. After leaving the agency, his wife says, he worked as a security consultant specializing in cigarette smuggling.
Last week, Undersecretary for Political Affairs William Burns, the State Department's third-ranking official, met with Levinson's family, and earlier this fall, the State Department sent a diplomatic note to Tehran through the Swiss government, which represents the U.S. interests in Iran in the absence of an American diplomatic presence in the country.
In September, Christine Levinson flew to the United Nations in New York to ask questions about her husband.
She sought a meeting with Iranian President Mahmoud Ahmadinejad, who was at the United Nations for the U.N. General Assembly. But Ahmadinejad declined to meet with her.
Last year, she traveled to Iran to try to retrace her husband's steps. Back then, Iranian officials told her they would investigate and report back to her. She still hasn't heard a word.
The State Department and FBI have denied he was working for the government and has demanded that Iran free Levinson -- if it is holding him.
Levinson says her husband suffers from diabetes and high blood pressure and has offered a $5,000 reward for information leading to his safe return.
Last year, CNN reported that Levinson met with Dawud Salahuddin, an American fugitive who lives in Iran, shortly before his disappearance.
Salahuddin -- known in Iran as Hassan Abdulrahman -- converted to Islam and was given refuge in Iran after admitting in interviews to killing Ali Akbar Tabatabai, a former Iranian diplomat under the shah, in Maryland in 1980.
Salahuddin said he was detained by Iranian officials in plain clothes and taken away from the room he shared with Levinson to be interrogated about his Iranian passport.
When he was freed the next day, he said, he was told by officials that Levinson had returned to Dubai.
Senior administration officials have told CNN that they think Salahuddin met with Levinson, but do not believe him to be a credible source of information on Levinson's whereabouts.
McCormack said the State Department is trying to keep the public aware of the case in the hopes of finding a fresh clue about Levinson's whereabouts.
"We're always looking for ways to maybe break loose that vital piece of information or the vital lead that may help us," McCormack said.
He asked anyone with information about his case to contact the State Department or the Levinson family via their Web site.