British-American-Iranian wildlife conservationist Morad Tahbaz has ended his nine-day hunger strike he started after his abrupt return to prison despite pledges of furlough.

Human Rights Watch said on Monday that Iranian authorities should immediately and unconditionally release him and other environmentalists wrongfully imprisoned with him.

The tri-national, in detention since January 2018, was left behind when two other British hostages -- Nazanon Zaghari-Ratcliffe and Anoosheh Ashuri -- were released by the Islamic Republic in exchange for a 400-million-pound UK debt to Iran.

The British Foreign Secretary Liz Truss claimed credit for negotiating a furlough for Tahbaz. Iranian authorities first released him on March 16 and allowed him to go to his family home in Tehran but detained him again two days later despite an apparent agreement between Iranian and British authorities to guarantee his leave, leading him to embark on a hunger strike.

Tara Sepehri Far, senior Iran researcher at Human Rights Watch, says, “It is abhorrent that Iranian officials continue to use dual and foreign nationals detained in Iran as bargaining chips. It is also particularly disappointing that British authorities did not do enough to ensure Iran would uphold the conditions they agreed to for Tahbaz’s furlough.”

In an interview published by BBC on Tuesday, Ashuri said, "Sometimes I think he should have been on the return plane instead of me. He is ill and needs medical attention”, adding that it's really painful that so many good people are left behind.