German Foreign Minister Frank-Walter Steinmeier (L) French Foreign Minister Laurent Fabius (3rd L) Chinese Foreign Minister Wang Yi (4th L) European Union High Representative for Foreign Affairs and Security Policy Federica Mogherini (centre row, 2ndR) US Secretary of State John Kerry (4th R) British Foreign Secretary Philip Hammond (3rd R) and Russian Foreign Minister Sergey Lavrov (R) meet in Vienna, Austria July 7, 2015. [Photo/Agencies]

Referring to sticking points remaining in the talks, French Foreign Minister Laurent Fabius told reporters: "As far as France is concerned, we are insisting especially on necessary limitations on nuclear development and research, sanctions and their re-establishment, and the possible military dimensions" of past Iran's nuclear research.

Officials and experts from Iran and P5 plus 1 countries are now busy discussing some eight technical issues needed to be agreed on before diplomats proceed with further steps towards a general nuclear agreement, Lavrov told reporters, noting that the "polishing" of these issues will take a day or two.

China remains confident about reaching a final deal in this round of talks. Despite of around six or seven remaining issues, "all sides realize that this is the last negotiations," said Wang Yi, the Chinese foreign minister.

Meanwhile, some foreign ministers are leaving on Tuesday, but will come back to Vienna in the coming hours or days, said Mogherini.

Iran and five United Nations Security Council permanent members plus Germany missed the previously-set June 30 deadline for a comprehensive deal. Both sides agreed to extend the deadline to July 7.

All parties have been negotiating over the past 16 months to reach a long-term deal over Tehran's disputed atomic plan.