Four United Nations human rights experts launched a fresh appeal Friday for Iran to annul the death sentence given to university professor Ahmadreza Djalali, accused of passing information to Israel.
The renewed call came days after Iran's Supreme Court reportedly rejected a request to review the sentence.
"We urgently call on Iran to lift the death sentence imposed on Dr. Djalali, as the state has apparently not complied with its international obligations to give him a fair trial and the right to appeal," the experts said in a joint statement.
Djalali, a specialist in emergency medicine resident in Sweden, was detained in April 2016 after a brief visit to Iran.
He was found guilty in October of passing information about two Iranian nuclear scientists to Israel's Mossad intelligence agency that led to their assassinations.
His death sentence has been widely condemned by rights groups including Amnesty International.
The four experts include Jose Antonio Guevara Bermudez, who heads the UN working group on arbitrary detention and Nils Melzer, the UN special rapporteur on torture.
Agnes Callamard, an expert on summary executions and Asma Jahangir, the special rapporteur on human rights in Iran, also co-signed the statement.
They renewed a call first issued in December for Djalali's immediately release.
A total of five Iranian scientists -- four of them involved in the country's nuclear programme -- were killed in bomb and gun attacks in Tehran between 2010 and 2012 at the height of tensions over the country's nuclear ambitions.
Iran has accused Mossad and the CIA of ordering the killings.