The White House said on Thursday the United States would continue to have diplomatic talks with Iran about a nuclear deal.

"Our view is that we are close. We have been close for some time now," White House spokesperson Jen Psaki said. "The end of negotiations is always when the difficult and challenging parts of the conversation typically take place."

Iran has refused to hold direct talks with the US. European countries and Russia have been acting as mediators in Vienna talks that began almost one year ago.

The United States and other participants in the Vienna talks have been repeatedly saying a deal is close in recent weeks. However, multilateral, formal session have ended in Vienna as diplomats say the time has come for political decisions.

The details of what issues still remain unresolved are not known, but Iran apparently has been demanding that its Revolutionary Guard be taken out of the US Foreign Terrorist Organization (FTO) designation.

Russia on Saturday introduced a new complicating factor into the already complex situation by demanding that its economic and other relations with Iran be exempted from sanctions imposed for of its invasion of Ukraine.