Washington -- The wife of a former FBI agent who vanished in Iran in 2007 expressed bitter frustration Thursday about efforts to get her husband back home. Christine Levinson told a House panel that she holds Iran responsible for the disappearance of her husband, Robert, but she also said three American administrations have failed to press the Tehran government hard enough for his return.

"Time and time again, Bob has been left behind, deprioritized, or seemingly forgotten," she said at a House hearing on the status of Americans detained in Iran.

Robert Levinson vanished while in Iran on an unauthorized CIA mission. Christine Levinson said she believes her husband is alive and that the U.S. should press Iran harder for answers. She praised the work of "some dedicated people from various agencies" but said others in the government have not communicated with each other regarding his case, or have questioned whether he is alive and have undercut efforts to secure his release.

"My husband served this country tirelessly for decades," she said. "He deserves better from all of us and from our government. He deserves our endless pursuit to bring him home, to fight day and night and leave no stone unturned."

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In a statement released Friday, one day before the 12 year anniversary of Levinson's disappearance, U.S. Secretary of State Mike Pompeo said renewed his department's "call on the Government of the Islamic Republic of Iran to return Mr. Levinson to his family. Representatives of Iran and the United States previously agreed to cooperate on locating and recovering Mr. Levinson. Iran must honor this commitment, and demonstrate its adherence to international norms and respect for human rights."

Pompeo said the U.S. government remained "unwavering in our commitment to reunite the Levinson family with their beloved husband and father, who served our great nation during a long and distinguished career."

Christine Levinson testified along with Babak Namazi whose Iranian-American father and brother, Baquer and Siamak Namazi, are both serving 10-year sentences on espionage charges. Omar Zakka also told lawmaker about his father, Nizar Zakka, a Lebanese-born U.S. permanent resident who was detained after he visited Iran in 2015 to attend a conference.

Babak Namazi said that more than two years after President Donald Trump took office, "it seems that we are not any closer in getting my family and other hostages home." He said time is running out for his 82-year-old father. The elder Namazi's health is rapidly deteriorating and needs to leave Iran for medical attention, the son said.

There are at least five Americans being held in Iran in addition to one U.S. permanent resident. The United Nations said last year that arrests of Americans in Iran are part of an "emerging pattern" by Tehran targeting dual nationalities.

On Friday, CBS News learned that one of the Americans most recently detained by Iran, U.S. Navy veteran Michael White, 46, had begun a hunger strike to protest his detention.

Iranian cyberactivist Ivar Farhad told CBS News that White began a hunger strike on Thursday. He said in a tweet that White was protesting "his uncertain situation and anti-human condition" of his detention. It was Farhadi who first broke the news in December of White's imprisonment, tweeting that he had met the California native in prison in the Iranian city of Mashhad.

White worked as a cook for the Navy and left the service about a decade ago, according to a spokesman for his family. Both his family and U.S. officials have insisted White was not a spy. The spokesman, Jonathan Franks, said White had recently worked as a janitor.

White's mother Joanne told CBS News in January that she prays every day that her son will be freed from prison in Iran before it's too late. She said she worried his recurring cancer could come back and he could die. Joanne White has said her son was on his third trip to visit a girlfriend in Iran in July when he was arrested.

An Iranian judicial official has said White is being sued by a private plaintiff, referring to a complaint by a citizen, not the government, but the official did not rule out possible "security-related charges."

On Thursday, Namazi told the U.S. lawmakers that he was "counting on President Trump to stay good to his word that Americans will not languish in Iran when he is president," citing the administration's recent successes freeing American hostages in other countries. "I implore the president to spare no effort to bring my family and the other American hostages home from Iran."

A hard line on Iran has been central to Trump's foreign policy, including withdrawing from a landmark nuclear deal and reinstating economic sanctions. He has pledged "serious consequences" if Americans detained in Iran are not returned.

Dan Levinson, Robert's son, said his family has been more hopeful following the reimposition of sanctions.

"We believe after dealing with the Iranians for 12 years now that they only respond to pressure and we think that it's the only way to bring them to the negotiating table," he told reporters before the hearing.

Levinson was a contractor for the CIA who traveled in March 2007 to an Iranian island, Kish, where he met with a U.S. fugitive. He has not been seen since except in a video sent to his family by his captors. His wife said in her testimony that an FBI assessment of the video and photos showing him in an orange jumpsuit concluded that the Iranian government must have developed them and sent them to the family. "All the facts of the case indicate they kidnapped my husband," she said.

Levinson, the longest-held hostage in U.S. history, was not part of a prisoner exchange deal that former President Barack Obama struck with Iran in 2016. That swap saw four other Americans freed from Iranian prisons in exchange for seven Iranians held or charged in the United States.

Iran has said Levinson is not in the country and that it has no further information about him.

Rep. Ted Deutch, chairman of the House Foreign Affairs subcommittee that held the hearing, asked the family members what their message would be to Mr. Trump.

"I would ask that he would meet with us," Christine Levinson said. "He doesn't know us. He doesn't understand how difficult it is for us."

After the hearing, Deutch, D-Fla., and three other members of Congress introduced legislation that would empower the president to impose sanctions on hostage-takers, elevate the special presidential envoy for hostage affairs to the rank of ambassador, and create an interagency group that would work on hostage recovery and response.