US officials believe Robert Levinson may no longer be in Iran, a White House spokesman said today, vowing that the US 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 US 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.