Several of the remaining major importers of Iranian crude have made fresh deep cuts in their purchases in order to satisfy agreements with the US, even as hopes of a breakthrough in talks on Tehran’s nuclear programme rise.

The moves by customers including China and South Korea, which for months have provided an economic lifeline to the Islamic republic, will increase the pressure on Iran to accept a deal from western powers.

Oil exports provide half of the Iranian government’s revenues and account for 80 per cent of the country’s total exports, according to the US Department of Energy.

Data cited by the International Energy Agency indicate Iran’s crude exports declined by 45 per cent last month to 715,000 barrels a day, the lowest level since January 2012 when the US imposed a stricter sanctions regime.

The drop in oil exports had forced Iran to cut its oil production this year to a low of 2.58m b/d, a level last seen in 1989 when Tehran was grappling with the impact of the Iran-Iraq war.

China, the biggest buyer of Iranian crude, slashed purchases by 47 per cent to 251,000 barrels of oil per day in October, according to customs data released earlier this week.

China, India, Japan, and South Korea have continued to import large volumes of its crude after the US granted waivers allowing them to scale back rather than end oil purchases.

However, they have to keep reducing shipments to extend waivers to US sanctions. China needs to make huge cuts to its imports over the last quarter of the year to meet its targets, according to analysts. The waivers are set to be reviewed before the end of the year

Falling exports are a blow to Iran, which is desperately short of foreign currency reserves and is facing an increasing struggle to place its barrels in the international markets.

In an effort to stimulate demand the National Iranian Oil Company (NIOC) is reportedly offering free delivery of crude exports to India and also extended payments terms. Unlike China and South Korea, India reduced its imports of Iranian oil in the first nine months of the year.

David Fyfe, head of market research at Gunvor, a Swiss trading house, said Iranian exports appeared to have recovered, running at around 1.1 to 1.2m b/d so far in November, having fallen below 1m b/d in the previous two months. "We may see production stabilise in November if exports are anything to go by,” Mr Fyfe said.

Iranian production fell to 2.58m b/d in September, a sanctions-era low, and the country’s lowest output since May 1989, when its oil industry was still recovering from the Iran-Iraq war. It recovered slightly to 2.68m b/d in October.

Other traders said Iran was unlikely to “shut in” production further, despite the difficulties the country is facing in finding a home for its oil. A market for very large crude carriers (VLCCs), which can be chartered at relatively low rates, may be encouraging Iran and its buyers to turn once again to floating storage.

The IEA reckons around 300,000 b/d were moved into floating storage in October, bringing the total volumes unsold on ships to 37m barrels of oil, some located off the coast of China.

In addition, the pressure on Asian buyers to reduce Iranian purchases could quickly end were there to be a breakthrough on the Iranian nuclear talks.

"If there is a deal in Geneva, some remaining Asian oil buyers might see it as writing on the wall that oil sanctions are going to be eased and conclude they can increase imports from Iran without being denied a waiver by the State Department,” said Bob McNally a former US government official and head of the Rapidan Group.

Fereidun Fesharaki, head of the Facts Global Energy consultancy, said Iranian exports to Asia could climb by 200 too 400,000 b/d very quickly, if restrictions on insuring Iranian ships were eased as a result of a breakthrough in talks, even without a wider unwinding of sanctions.