"Mr. Levinson will remain a priority for the United States until he is reunited with his family," State Department spokesman Philip Crowley said, reading a statement on the anniversary of his disappearance.
The mystery of Levinson's disappearance is a further strain in US-Iranian relations, which remain tense over Iran's nuclear drive and the fate of other Americans held there.
Levinson is "desperately" missed by his family, Crowley said, adding he is a father of seven children and grandfather of two, one of whom was born in his absence.
Christine Levinson says her husband, who retired from the FBI more than a decade ago, had traveled to Kish island to investigate cigarette counterfeiting in the region and was last heard of on March 8, 2007.
The Iranian officials had shown Christine Levinson "a willingness to share information about their investigation into her husband's disappearance," Crowley said.
"We ask that Iran stand behind its commitment to provide full details about their authorities' investigation," the State Department spokesman said.
"The United States also calls on Iran to resolve the cases of the five American citizens who are unjustly detained in Iran: Joshua Fattal, Shane Bauer, Sarah Shourd, Kian Tajbakhsh, and Reza Taghavi.
"We ask anyone who may have information about Mr. Levinson to contact us or the Levinson family via their website: www.helpboblevinson.com," Crowley said.
