US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif are trying to meet a Tuesday deadline for a final deal under which Iran would curb its atomic work for more than a decade in exchange for sanctions relief.

Riding on its long-standing relationship with Tehran and fuelled by geopolitical interests, Beijing has branded itself as a neutral arbitrator in the negotiations.

Although still widely seen as a low-profile member of the six-nation talks, Chinese foreign minister Wang Yi's presence in key negotiations, Chinese analysts said, was an indication that China has been actively engaged.

Despite criticism that China’s close relations with Iran – largely buoyed by energy and economic cooperation – could complicate the talks, Chinese analysts said Beijing had a lot of interests in seeing the deal succeed.

Helping Tehran end the 13-year Western isolation would not only allow Chinese investment to operate more freely in Iran, but could also stabilise the Middle East, said Zhao Tong, an associate at Carnegie’s Nuclear Policy Programme based at the Carnegie-Tsinghua Centre for Global Policy.

“China has every reason to welcome a stable and peaceful Middle East, because its One Belt One Road goes through the Middle East,” Zhao said, referring to a government strategy to expand China’s economic footprints across Eurasia.

China has long been a major buyer of Iranian oil, which accounts for roughly 12 per cent of the country’s annual consumption. Last year, its imports from Iran increased by 28.3 per cent to the highest average level since 2011.

Many analysts have said that by providing an important lifeline to the Iranian government, China’s trade and energy deals could reduce incentive for Tehran to compromise for a nuclear agreement.

“But given the fact that China has repeatedly sided with Western countries in imposing international sanctions on Iran, its reliability has been questionable,” said Ali Vaez, a senior analyst on Iran with the International Crisis Group.

“Iran appears eager to establish a strategic relationship with China, but so far China has preferred to hedge its bets in the Persian Gulf region.”

China has said its role in the negotiations has been constructive in its own ways. Li Bin, a former nuclear negotiator and now a senior associate at Carnegie Endowment for International Peace, said Chinese diplomats had served to bridge the gaps between Iran and Western powers when negotiations broke down.

But Vaez said China was still far from being proactive in the negotiation process. “The heavy lifting [in the negotiations over the past two years] has been done by Iran, the United States and the European Union,” he said.

A major sticking point in the negotiations has been the inspection of military nuclear sites. The six-nation negotiating group, known as P5+1 – US, China, France, Russia, Britain, and Germany – have insisted that inspectors from the International Atomic Energy Agency should be given access to Iranian military sites where nuclear and nuclear-related facilities are believed to be located.

Allowing inspectors from states that are hostile to it has been an uncomfortable idea for Iran, Vaez said. “Assassination of Iranian nuclear scientists and cyberattacks on its facilities have exacerbated these fears,” he said.

One possible solution for the impasse, according to former French diplomat Jean-Christophe Iseux von Pfetten, is for China to play a bigger role in the IAEA inspection into the military sites.

Given China’s better relations with Iran, Von Pfetten said Iran would be more willing to let a Chinese-led inspection team into its military sites.

A backdoor diplomatic meeting is being organised to encourage China to take the lead in the military site inspection, said Von Pfetten, who has organised similar meetings on Iranian nuclear issues before.

The French baron, who is also the president of the Royal Institute for East West Strategic Studies, said that a top Chinese defence ministry official and a former defence minister had agreed to attend the meeting, but he refused to reveal their names.

Mahmoud Mohammadi Araghi, a member of Iran’s Supreme Council of Cultural Revolution, would also attend the meeting, likely to last two to three days.

According to Von Pfetten, Iran has said it would not allow inspectors from the US into its military sites, and instead it would prefer China to lead the inspection.

“The US is happy to let China take the leading role,” he said. “But what is more difficult [for the US] to accept is to have no Americans in the inspection team.”

Major General Xu Guangyu, a senior consultant to the China Arms Control and Disarmament Association, said China would be willing to take up the role as long as the inspection would not interfere with Iran’s domestic affairs.

With additional reporting by Reuters