In a meeting between negotiating teams from Iran and the Group 5+1 (the five permanent UN Security Council members plus Germany) in Vienna's Coburg Hotel, the group stressed the necessity for reaching an agreement on schedule, the Iranian Foreign Ministry's Director General for the Political and International Affairs Hamid Baeidinejad wrote on his Instagram page on Thursday.

In the session, the members of G5+1 (alternatively known as the P5+1 or E3+3) described the resolution of the remaining issues over Tehran’s nuclear program as complicated and time-consuming, and asked for intensive planning for the talks in the remaining days, he stated.

The plenary session of nuclear negotiations held in Vienna on Thursday at the deputy ministerial level.

Two Iranian deputies foreign minister, Abbas Araqchi and Majid Takht Ravanchi, represented the Islamic Republic in the meeting with their counterparts from Russia, China, the US, Britain, France and Germany.

Before the plenary session, the Iranian diplomats had met with the European Union's deputy secretary general for the external action service, Helga Maria Schmid.

Iran and the Group 5+1 resumed drafting the text of a final agreement, known as the Joint Comprehensive Plan of Action (JCPOA), on Thursday.

The two sides have held several rounds of talks in recent months to hammer out a lasting accord that would end more than a decade of impasse over Tehran's civilian nuclear program.

On April 2, Iran and the sextet reached a framework nuclear agreement in Lausanne, Switzerland, with both sides committed to push for a final deal until the end of June.