By ERIC TUCKER, Associated Press

WASHINGTON (AP) — Families of several U.S. and British people held in Iran expressed fear for their loved ones Tuesday amid the deadliest unrest in decades in the Islamic republic.

The relatives spoke at a news conference in Washington to demand the release of spouses and parents held in Iran — in at least one case for more than a decade. Among those who spoke was a daughter of Robert Levinson, the former FBI agent who disappeared in Iran in 2007.

The protests now roiling Iran, reflecting widespread economic discontent and outrage over spiking gasoline prices, have been an added challenge to families who have gone years without seeing their loved ones. Iranian state television acknowledged Tuesday that security forces shot and killed protesters in multiple cities.

“Of course any kind of protest that goes on in Iran, and any kind of situation, that overlaps potentially with the fact that our families and loved ones are being held there as well," said Babak Namazi, whose brother and father are held captive in Iran. “We've been talking about the brutality of what our family members have been facing. But I guess this is just a reminder of what the abilities and capabilities are.”

Prisons are more overcrowded now because of the demonstrations, the internet has been down, and communication has been even more complicated than it already is, Namazi said.

Sarah Moriarty, one of Levinson's seven children, said she was heartened by Iran's recent acknowledgment that it had an open case before its Revolutionary Court after years of denying any involvement in his disappearance.

Moriarty said she interpreted the development as Iran's first acknowledgment that it had indeed taken Levinson into custody, though Iran has also said it regards Levinson's case as a “missing person” file. She said she believes it's clear that Iran knows where her father is and is in a position to send him home immediately.

“This is incredibly significant because it means that they have a case against my father, and it means that they have him,” Moriarty said. “And we want to see him, and we want him to be released immediately."

Nearly two dozen of Levinson's relatives are expected in a Washington court this week to testify in a lawsuit that seeks to hold Iran responsible for the capture. The U.S. government, meanwhile, is offering up to $25 million for information leading to Levinson's rescue.

“We want Iran to know that this is not acceptable, and a big portion of our lawsuit is punitive damages because we want them to discourage them from doing this practice to anyone else,” Moriarty said.

Levinson disappeared from Iran’s Kish Island on March 9, 2007. For years, U.S. officials would only say that Levinson, a meticulous FBI investigator credited with busting Russian and Italian mobsters, was working for a private firm on his trip.

In December 2013, The Associated Press revealed that Levinson in fact had been on a mission for CIA analysts who had no authority to run spy operations.

Also present for the news conference was Richard Ratcliffe, whose wife, Nazanin Zaghari-Ratcliffe, is a British-Iranian charity worker held in Iran for more than three years. He said that though different Western nations have their own approaches to hostage negotiations, “none of them have worked."

He said sanctions should be considered as one option of punishment for hostage taking.

“There should be a real clear cost to hostage taking," he said. “It should be an anathema in the modern world."