Swiss and Austrian investigators have launched probes into alleged spying in hotels hosting delicate Iranian nuclear talks, the authorities in both countries said Thursday.

The Swiss attorney general's office confirmed it had launched an investigation on May 6 and conducted a raid six days later, seizing computer equipment, due to "suspicion of illegal intelligence services operating in Switzerland."

It did not specify if hotels were targeted in the probe.

"The aim of this raid was on one hand to gather evidence and to on the other verify if information systems had been infected by malware," the attorney general's office said in an email.

The revelation comes in a countdown to a June 30 deadline for a historic agreement between Iran and world powers on curtailing Tehran's nuclear programme in return for relief from punishing sanctions.

Austria -- which has also hosted numerous rounds of the nuclear talks -- said Thursday it was also investigating possible spying at meeting venus there.

"Investigations are ongoing" regarding the Palais Coburg hotel, the location of many rounds of the talks including discussions this week, interior ministry spokesman Karl-Heinz Grundboeck told AFP.

Recent talks in Geneva held at the luxury Intercontinental Hotel failed to bridge differences between Washington and Tehran, especially over the crucial issue of inspections of military sites.

The talks between Iran and the world powers have been held in several Swiss hotels: the Palais Wilson and Intercontinental in Geneva, the Beau Rivage in Lausanne and the Royal Plaza in Montreux.

Thursday's announcement came after a Russian-based security firm said Wednesday the malware dubbed Duqu, which is a sophisticated spy tool that was believed to have been eradicated in 2012, appeared to have been used to spy on nuclear negotiations with Iran.