Iranian senior nuclear negotiator Abbas Araqchi said talks are not in a stage to require the presence of foreign ministers of other members of 5+1 member states, IRNA reported.
Talking to IRIB, he said there is of course nothing to hinder their presence in the talks if they wish so.
However, he added, negotiations have not reached the state yet to demand the presence of the foreign ministers of all 5+1 member states.
Araqchi stated that negotiations have not reached the point where we could say it is the end so other foreign ministers too should join us.
He explained that the US is now participating in the talks in the foreign ministerial level while others have sent their foreign minister deputies to the talks.
Araqchi said Iran is not going to restrict itself to any dates though a seven month period has already been set for finalizing the talks with the end of the March being chosen as the date for developing the preliminary agreements.
Meanwhile, Iran's Foreign Minister Mohammad Javad Zarif said on Thursday that he will stay in Lausanne as long as it is required to negotiate over a deal on Iran's peaceful nuclear program.
'Currently, we see ourselves in the final stage of negotiations that requires more intensive talks,' Zarif said.
Zarif also said that negotiations are very complicated. However, he noted that they are making good progress.
Zarif and the US Secretary of State John Kerry held their sixth round of talks in Lausanne today to bridge the gulf over Tehran's peaceful nuclear program.
Apart from Abbas Araqchi, Majid Takht Ravanchi and Wendy Sherman, the deputy foreign ministers of Iran and the US who attended the meeting, head of the Atomic Energy Organization of Iran Ali-Akbar Salehi and US Secretary of Energy Ernest Moniz, as well as Hossein Fereidoun, a special advisor to President Hassan Rouhani were present at the talks.
Earlier in the day, Salehi and Moniz had discussed the remaining technical differences.
The Iranian negotiators are in talks with their US and European counterparts in Lausanne since Sunday.