VIENNA, May 16 (Xinhua) -- The forth round of Iranian nuclear talks ended Friday in Vienna, making "no tangible progress," but the negotiation will continue in coming months, Iran's chief nuclear negotiator was quoted as saying.

Abbas Araqchi, who is also Iranian deputy foreign minister, on Friday made the remarks after a 3-day meeting with five permanent members of the UN Security Council (China, France, Russia, the UK and the United States) and Germany in Vienna.

Araqchi believes "drafting" could be started "when the positions are closer to each other," without providing further details of the talks.

Before the talks, U.S. and Iranian officials said the talk could be "very difficult" as the significant gap between Tehran and west remains.

Western states suspect Iran has been developing atomic weapon undercover of its civilian nuclear plan, while Iran dismisses the allegation, saying its nuclear program is solely peaceful and the allegation is baseless.

It has been assumed that big gaps are still not bridged in terms of key issues between Iran and western countries in the talks, including the nuclear fuel fabrication capability, transparency of Iran's nuclear plan and Iran's ballistic missile program, as western countries see these as crucial elements in building a nuclear warhead.

Western states want Iran to significantly scale back its nuclear plan to meet western concerns, but Iran said it have the right to develop peaceful nuclear program under the Non-Proliferation Treaty.

Wang Qun, head of China's delegation, director general of Chinese Foreign Ministry's arms control and disarmament department, said in Vienna that the Iranian nuclear talks has already enter a "deep-water zone", thus the negotiation is like "crossing a river by feeling the stone."

When asked about if any progress were made in the talk, he stressed the importance of this round of talks is to deepen the understanding of the sides on the substantive issues in this process.

Under the Geneva deal made in last November, Iran suspends some of its nuclear activities while western states relief some relevant sanctions in return.