Iran's envoy to the U.N. nuclear watchdog agency says Tehran is not surprised by reports that a cyber-espionage campaign targeted hotels that hosted nuclear talks between Iran and world powers.

Reza Najafi told Iran's state TV on Thursday that Iranian nuclear negotiators took "precautionary measures" to protect their secrets.

Kaspersky, a cybersecurity firm with close ties to Russian intelligence, said Wednesday the malware it uncovered was so sophisticated, it must have been created by a government.

Citing former U.S. intelligence officials, The Wall Street Journal attributed the spying to Israel, which opposes the emerging nuclear deal between Iran and world powers.

Negotiators hope to clinch a final accord by the end of the month to curb Iran's nuclear activity for a decade in exchange for lifting sanctions.