Washington says talks between Iran and the US on Tehran’s nuclear energy program is not an indication that a broader rapprochement between the two countries on other issues is underway.

Iran and the P5+1 group of states – the United States, Britain, France, China, Russia, and Germany – are holding negotiations to narrow their differences on the outstanding issues related to Tehran's nuclear program ahead of a July 1 deadline for the final agreement.

On Wednesday, US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif wrapped up a third day of “intense” negotiations between Tehran and Washington in the Swiss city of Montreux.

"Even as we negotiate, this in no way represents a broader warming of ties, lessening of concerns on our part. This is not about a broader rapprochement in any way. This is about the nuclear issue and that's it," US State Department spokeswoman Marie Harf said.

"We are not linking the nuclear agreement or a successful nuclear agreement to a broader warming of ties, to a broader rapprochement on other issues, or in general," she added.

Relations between Washington and Tehran collapsed after the 1979 Islamic Revolution, because the US had been backing former Iranian dictator Mohammad Reza Pahlavi.

In November 1979, a group of Iranian university students stormed the US embassy in Tehran, also known as the “den of espionage”.

The students believed the US mission had turned into a center of spying aimed at overthrowing the Islamic establishment in Iran following the Islamic Revolution earlier that year.

Documents found at the compound later confirmed claims by Iranian students that Washington was using its Tehran embassy to plot to topple the new Islamic establishment of Iran.

The State Department spokeswoman said that “rapprochement” between the US and Iran “would indicate or would suggest some broader warming of ties…”

"I can't predict what would happen in two or five or 10 or 15 years, and the president, separately from the nuclear negotiations, has spoken multiple times about some day we would like to have a different relationship with Iran," she stated.