The foreign ministers of six major world powers are set to hold intense negotiations in Geneva hoping to secure a nuclear deal with Iran ending a decade-long standoff.
Chinese, British, French and German foreign ministers will join their Russian and Iranian counterparts who are already in the Swiss city.
Diplomats have expressed the hope that this round of talks will yield a breakthrough in sealing the deal as major thorny issues are said to have be resolved over the last three days of talks by top officials.
Iran is pushing for easing of economic sanctions in return for curtailing some uranium enrichment activities. Top delegates from the countries have been involved in the talks which were extended after a possible breakthrough was in sight.
The Guardian quoted Iranian foreign minister Mohammad Javad Zarif as saying: "In some cases a number of phrases have been added [to the text] and we still need to do some work in other cases. We are dealing with an issue that was the subject of difference for 10 years."
British foreign secretary William Hague had earlier said that the differences were narrow which could be sorted out with political will and commitment.
"We have made progress, including core issues," a senior European diplomat told reporters, pointing out the arrival of foreign ministers in Geneva signals they are on the verge of signing the deal.
Both the US and China have also articulated similar optimistic views. US State Department spokesperson Marie Harf told reporters that secretary of state John Kerry will reach Geneva "in light of the progress being made... with the hope that an agreement will be reached".
China's foreign ministry spokesperson Hong Lei said, according to the official Xinhua news agency, the discussions have "reached the final moment". Chinese foreign minister Wang Yi had missed the previous round of talks with Iran.
The decision to have the physical presence of the foreign ministers of all the countries involved in the talks was made following consultations with European Union foreign policy chief Catherine Ashton, who is coordinating the Geneva conference.
"You know our position ... it's a position based on firmness, but at the same time a position of hope that we can reach a deal," said French foreign minister Laurent Fabius, who took a hard-line position during earlier rounds of talks.