Josep Borrell, the European Union's top diplomat, confirmed that Johan Floderus, a Swedish diplomat working for the EU, has been captive in Iran for more than 500 days and said the bloc is working to secure his release.
"I want to stress that I personally, all my team at all levels -- European institutions in close coordination with the Swedish authorities, which have the first responsibility of consular protection -- and with his family, have been pushing the Iranian authorities to release him," Borrell said at a meeting on development in the Spanish city of Cadiz on September 5.
"Every time we had diplomatic meetings, at all levels, we have put the issue on the table. Relentlessly," he added.
A day earlier, Sweden and the EU announced that a 33-year-old Swedish national was detained in what is the latest known case of a foreigner being held there amid political tensions with the West.
Neither originally released Floderus's name, but the New York Times, quoting diplomatic sources, identified Floderus as the diplomat behind bars.
Iranian Foreign Ministry spokesman Nasser Kanani said on September 4 that he did not know about the case. The Intelligence Ministry, however, said a Swedish national had been included on a list of "suspects" of a counterespionage unit due to "some suspicious behavior and communications" during previous trips to Iran.
Iranian security forces have taken some 40 foreign nationals into custody during the current wave of unrest, often without revealing any charges.
Western countries have repeatedly said Iran is trying to take advantage of foreign countries by taking dual and foreign nationals hostage to use in prisoner swaps.
Relations between Tehran and Stockholm have been strained further in recent months after a man tore up and burned a Koran outside a mosque in the Swedish capital in July. In protest, Iran has refrained from sending a new ambassador to Sweden.