More dual-citizens would be seized and wrongfully jailed in Iran if the US fails to link the fate of foreign hostages to restoring the Iran nuclear deal, a coalition of families told President Joe Biden’s administration.

All prisoners must be freed and Tehran must commit to end “hostage-taking” as a condition of resuming the Joint Comprehansive plan of Action, a letter signed by 20 families of detainees and former inmates said.

Efforts to bring the US back into the 2015 deal will be stepped up on Tuesday as the five world powers remaining in the accord meet Iranian officials in Vienna. The US and Iran will start talks through intermediaries.

The group behind the letter – Hostage Aid Worldwide – said the release of US prisoners was “anything but a priority” for Mr Biden’s administration before resuming the nuclear deal. At least 16 US and European dual citizens are held by Iran.

Richard Ratcliffe, the husband of aid worker Nazanin Zaghari-Ratcliff, who remains in Tehran  despite completing her five-year jail term on trumped-up espionage charges, said Tuesday’s talks were an opportunity to make amends after a series of failures in dealing with Iran.

“Western diplomats should be in no doubt when they sit down on Tuesday that the hostages need to come home first, or else more lives will be collected and it will continue to become more complicated to bring them home,” he said.

Former president Donald Trump pulled the US out of the accord in 2018, opting for what he called a “maximum-pressure campaign” of sanctions.

Since then, Iran has been steadily breaking the restrictions of the deal, such as the amount of enriched uranium it can stockpile and the purity to which it can be enriched.

Tehran’s moves appear calculated to put pressure on the other nations in the deal – Russia, China, France, Germany and Britain – to do more to offset the sanctions reimposed by Mr Trump.

Upon his inauguration, Mr Biden said that returning to the accord to limit Iran’s nuclear programme was a priority.

The countries are at odds over Iran’s demands that sanctions are lifted first.

“No Iran-US meeting. Unnecessary,” Iranian Foreign Minister Javad Zarif wrote on Twitter.