VIENNA, July 14. /ITAR-TASS/. There is no progress on key issues at the talks with the USA in Vienna so far, Iran's Deputy Minister of Foreign Affairs Abbas Araghchi told journalists on Monday.

"The negotiations with US Secretary of State John Kerry were difficult but useful," he noted. "However, there is still no progress on key issues."

US Secretary of State John Kerry gave a similar assessment to the consultation process. "It is a really tough negotiation I will tell you," he stressed in a conversation with journalists. "We are in the middle of talks about nuclear proliferation and reining in Iran's program."

Meanwhile, a diplomatic source in one of the delegations reported that US High Representative for Foreign Affairs and Security Policy Catherine Ashton, Iran's Foreign Minister Mohammad Javad Zarif and US Secretary of State John Kerry would hold a tripartite meeting in Vienna late on Monday. "I can confirm that the parties will hold such a meeting to consider the issues of the negotiating process in detail once again," the source said. "It may start in an hour already."

Kerry was said to be considering the possibility of staying in Vienna until July 15.

The source said the sides had reaffirmed their readiness to work literally 24 hours a day in a bid to bridge the gap in their positions as much as possible and reach a common result.

A member of the US delegation said earlier that one of the purposes of Kerry’s visit to Vienna would be conducting detailed consultations with his Iranian colleague in order to determine Tehran’s readiness to take critically necessary steps.