VIENNA - Iran and P5+1 group are striving to find a long-term solution for the decade-old disputed Iranian nuclear program, aiming to strike a comprehensive deal which could change the political map by deadline next Monday.

Negotiators from Tehran and so called P5+1 group(Permanent members of the UN Security Council plus Germany) are making last effort to bridge the gaps over some key issues.

Gaps still remain on some key issues, which include defining the size and scope of Iran's nuclear program, particularly the number of centrifuges Iran will operate during the duration of the deal, and the nuclear relevant sanction relief.

Some experts are expecting another interim deal instead of a comprehensive accord by the deadline as the issue could be too tough to resolve in this round of talks, while officials has been publicly insisting they would not discuss the extension of the deal at this moment.

The stakes of the talks are high, but on the other hand, once the deal is agreed, it could change the political map in Middle East.

The US announced that Secretary of State John Kerry would join the talks later this week.

Cheng Jingye, China's ambassador to UN nuclear watchdog on Tuesday said gaps remain in defining the scale of Iran's uranium enrichment.

Iran's nuclear program has long been suspected by western powers, who demanded Iran to significantly scale back its nuclear program to address the concerns, while Iran insists it has inalienable right to develop its civilian atomic plan.