U.S. officials believe Robert Levinson may no longer be in Iran, a White House spokesman said Tuesday, vowing that the U.S. would keep up the search for the former FBI agent who disappeared from an Iranian resort nearly nine years ago.

White House spokesman Josh Earnest said the U.S. has received assurance from the Iranian government it would search for Levinson. The commitment came amid broader negotiations over the return of several other Americans detained in Iran.

“We’re going to hold the Iranians to that commitment,” Earnest told reporters at the White House.

Levinson’s relatives said Monday they’re happy for the families of prisoners released from Iranian custody but wished government officials had warned them he would not be among them.

“We had to learn it from the TV ourselves, and that’s very disappointing and heartbreaking,” said Robert Levinson’s wife, Christine.

Robert Levinson disappeared from an Iranian resort on March 9, 2007, while in the country on an unauthorized mission for the CIA. It’s unclear where he is. Iranian officials have said they don’t know, but Levinson’s family does not believe them.

Earnest did not elaborate on the evidence putting Levinson outside of Iran. He acknowledged that if Levinson is no longer in the country, the Iran’s cooperation in the search may be limited use.

His son, Dan Levinson, told The Associated Press that it felt like “once again, he’s been left behind” and that the US can’t give up on bringing his father back.

Iran released four American prisoners over the weekend in exchange for the U.S. pardoning or dropping charges against seven Iranians. A fifth American was also released separately.

In discussing the release, President Barack Obama said the U.S. would continue working to find Levinson. But when asked by reporters whether Levinson was still alive, Secretary of State John Kerry said, “We have no idea.”

Levinson’s family insists he is still alive, even with health issues including diabetes, gout and high blood pressure. They last got some visual record of him in video and photos that were sent about five years ago.

“The people who are working on the case directly, they have told us there is no evidence to suggest my dad is not alive,” Dan Levinson said.

“We’re not going to give up because obviously we’re doing everything we can,” he said. “We need to make sure his country is doing the same.”

The family plans to mark Levinson’s upcoming birthday, which falls on March 10 — the day after the anniversary of his disappearance. It’s part of the way they’ve tried to cope with his absence.

“We talk about him all the time,” Christine Levinson said.

They’ve also tried to make his presence real for the three grandchildren he’s never met, teaching them a song Levinson came up with when his children were small.

“If you talk to the grandchildren, they all know how to sing the baby song,” she said.

Levinson’s family worries about what Levinson’s ordeal has done to a man who loved making friends and meeting people.

“I hope that he hasn’t lost hope,” Christine Levinson said.

(AP)