The families of three Americans and a British citizen imprisoned in Iran urged the U.S. government on Tuesday to apply more pressure on the Islamic republic for activities directly related to what they characterized as a hostage-taking industry.

The relatives said that the Trump administration’s “maximum pressure” campaign on Iran has not been sufficient in the cases of their loved ones, who have spent years behind bars in Tehran on charges their governments consider baseless.

Richard Ratcliffe, whose Iranian British wife, Nazanin, has been held for more than three years, called for new sanctions targeting anyone involved in wrongfully imprisoning foreigners. Most U.S. sanctions are imposed for activity related to other issues, such as terrorism, missile testing or nuclear activity.

“There is a new hostage crisis,” Ratcliffe said, describing a new wave of arrests by the Islamic Revolutionary Guard Corps. “And other countries are watching. They are looking closely — if a bad actor can get away with it, well then, why can’t we too?”

Ratcliffe was in Washington to speak with lawmakers on the Senate Human Rights Caucus and White House officials about the cases of foreign detainees in Iran. As on several previous trips, he was accompanied by a now close-knit group of families that have bonded over their shared ordeal.

Babak Namazi has spent four years trying to win freedom for his father, Baquer, and brother, Siamak, who were convicted of espionage-related offenses. Sarah Levinson Moriarty is one of seven children of Robert Levinson, who mysteriously disappeared in Iran more than 12 years ago. The Iranian government denies knowing what happened to Levinson but recently acknowledged having an open case on him in the Revolutionary Court, suggesting that he is alive and in custody.

“We don’t know if he’s had any human touch,” Moriarty said of her father.

Babak Namazi hinted at his disappointment that the Trump administration has not succeeded in obtaining freedom for his brother and father.

“President Trump has been saying leave no American behind, ‘America First,’ ” Namazi said. “We were counting on that. When he was a candidate in 2015, he promised that this will not happen when he is president, when my family was unjustly convicted. We’ve passed the three-year mark since that promise. And I hope and I pray and I expect that he will continue sparing no efforts to bring our loved ones home.”

Moriarty said the U.N. Security Council should take a clear stand on the cases. Her family has filed a lawsuit against Iran, and proceedings begin Wednesday in U.S. District Court in Washington.

“We have always believed over the past 12 and a half years, based on what we learned, that pressure works on them,” Moriarty said. “I think that we need to continue as much pressure as possible until they finally resolve these cases.”

The recent political unrest in Iran has complicated matters for the families. Communication has become more sporadic since the government temporarily shut down the Internet. Once telephone links were restored, their relatives said that more prisoners were being released to make room for newly arrested protesters — making those who are not set free feel even more despondent.

The families were accompanied by Nizar Zakka, a Lebanese citizen and U.S. permanent resident who was released last summer after spending nearly four years in prison in Iran.

Zakka said that during his detention, he had been surrounded by a “mini-United Nations” of prisoners from every continent, all imprisoned together at Tehran’s notorious Evin Prison. He said they were often blindfolded and mistreated. If they did not answer questions to an interrogator’s liking, they spent six weeks in solitary confinement, he said, only to return for another six-week stint if they had not changed their answers.

Zakka said the United Nations has taken no action against Iran for violating the 1979 International Convention Against the Taking of Hostages. “We are being played by the IRGC and the U.N.,” he said, referring to the Islamic Revolutionary Guard Corps.

Namazi family attorney Jared Genser rejected Iran’s claims that it is willing to negotiate for the prisoners’ freedom.

“These are all lies,” he said. “A total fabrication.”

Genser urged the imposition of sanctions under the Global Magnitsky Act, which is used for human rights abuses, against those implicated in hostage taking. He also said waivers on U.S. sanctions granted to allies that need Iranian oil should be conditioned on the release of prisoners.

Ratcliffe said the families will continue their campaign.

“All our cases are simple,” he said. “These are innocent people, being held as leverage. And that should not be allowed to go on.”