The EEAS, which brokers contacts with Iran on behalf of the “sextet” of international mediators, hoped to see the next round of six-party talks on Iran take place on January 28-29 in Istanbul, but Iran did not agree to the proposal.

“We have proposed a new date in February and we are waiting for a response from the Iranians,” Mann said.

Iran and the group of countries comprising Britain, China, France, Russia, the United States and Germany, known as P5+1, have held three rounds of talks over the Iranian nuclear issue last year, following a one-year break in the negotiations.

These talks, however, did not result in a breakthrough, as the sides cannot agree on the true nature of Tehran’s nuclear ambitions.

The United States, Israel and some of their allies accuse Iran of pursuing military objectives in its nuclear energy program.

Iran rejects these allegations, arguing that as a signatory to the nuclear Non-Proliferation Treaty and as a member of the International Atomic Energy Agency, it is entitled to develop and acquire nuclear technology for peaceful purposes.

Russia has repeatedly expressed concern over the slow pace of the nuclear talks with Iran, and stressed the need for the new meeting to be held as soon as possible.