The US says it has taken steps to ensure confidentiality of nuclear talks between Iran and major world powers, denying a report that Israel has been spying on the negotiations.

“We take steps, certainly, to ensure that confidential, that classified negotiating details stay behind closed doors in these negotiations,” State Department spokesman Jeff Rathke said Thursday.

“We are always mindful of the need… to take steps to keep our discussions confidential,” he added.

The Wall Street Journal reported Wednesday that European hotels hosting the closed-door negotiations were attacked by a virus widely believed to be used by Israeli spies. The Moscow-based cyber-security firm, Kaspersky Lab ZAO, discovered that three European hotels were targeted by a version of the spyware Duqu virus.

US officials and security experts believe Duqu, a virus first identified in 2011, was designed to carry out Israel’s most sensitive intelligence collection.

“The people behind Duqu are one of the most skilled and powerful [advanced persistent threat] groups and they did everything possible to try to stay under the radar,” said Costin Raiu, head of Kaspersky Lab’s Global Research & Analysis Team.

[caption id="" align="alignnone" width="650"] US Secretary of State John Kerry at the Beau-Rivage Palace hotel during a break in Iran nuclear talks in Lausanne, Switzerland, on April 1, 2015. (AFP photo)[/caption]

Rathke, however, said, “These are claims by a private company about another government, so we’re not going to weigh in on that report.”

According to the Journal, the Russian firm checked millions of computers worldwide after it discovered it had been hacked last year by the virus. While thousand of hotels that were tested found to be clean, three European hotels that had one thing in common found to be hacked.

Israeli officials refused to comment on the allegations relating to the hotel intrusions.

Israel “has denied spying on the US or Israel’s other allies, although they acknowledge conducting close surveillance on Iranians generally,” the Journal said.

Authorities in Switzerland and Austria, where the talks were held, launched an investigation into the spying.

During the investigations, the computers were seized due to “suspicion of illegal intelligence services operating in Switzerland.”

The US and the P5+1 group -- the US, Britain, France, China, Russia and Germany --are holding extensive talks with Iran to finalize a comprehensive nuclear agreement by the end of this month. The latest round of talks was held in the Austrian capital of Vienna this week.

By Press TV