The diplomatic deal on Iran’s nuclear programme has triggered a sell-off in crude prices as the geopolitical risk perceived by the oil market falls, but the actual impact on supplies is likely to be limited in the short term, according to analysts.

Brent crude, the global oil benchmark, fell as much as 2 per cent to $108.05 on Monday morning after Iran and six world powers agreed a deal on closer inspection of Iran’s nuclear programme in return for a limited easing of western sanctions on the country.

But key limitations on Iran’s oil sales, including a ban on exports to the European Union, remain in place. They will not be lifted unless the two sides can reach a final settlement during negotiations over the next six months.

In the short term, Iranian exports may receive a limited boost from current levels estimated by traders at up to 1.2m barrel per day, as the remaining large buyers of the country’s crude feel less pressure to reduce imports. However, a return to pre-sanctions levels of exports of around 2.5m b/d is not on the cards for now.

China, India, Japan and South Korea account for the vast majority of Iranian crude purchases, after the US granted them waivers from sanctions in return for reducing purchases.

China and South Korea have sharply cut imports in recent months in order to comply with those conditions, but may now act with less urgency, as the US State Department has pledged to allow purchases to continue at current levels over the next six months.

A key issue will be interpretation. A State Department fact sheet released shortly after agreement was reached in Geneva said Iran “will be held to approximately 1m barrels a day in sales”, which is somewhat below traders’ estimates of the current Iranian crude export levels. A text of the interim deal posted on an Iranian news website said western powers would “pause efforts to reduce Iran’s crude oil sales”.

Indian refiners may also increase imports if shipping and insurance sanctions are eased, as stated in the text on the Iranian site. Buyers, especially in India, have held back on purchases this year because of problems securing insurance. Indeed Rajkumar Ghosh, the director of refineries at Indian Oil, the country’s largest processor, told Reuters on Sunday: “We can go ahead and import the contracted volume for this year.”

However, Asian importers are unlikely to risk angering the US by significantly increasing imports, and other markets, including the EU, remain closed. The State Department was explicit in its post-agreement fact sheet that: “In the next six months, Iran’s crude oil sales cannot increase.”

All of which suggests the most bullish forecasts for oil supply growth next year – in which a return of Iranian production and continued rapid growth in US shale output leads to a sustained period of lower prices – still need to be treated with some caution.

It also means that while the Iranian deal will cast a shadow over next week’s meeting of the Opec in Vienna, it is unlikely to lead to a substantive change in the cartel’s policy for now.

We can expect Iran to make aggressive statements about its intent to regain market share. But the cartel, which tends to wait for changes in market conditions to materialise before changing policy, will probably take a wait-and-see approach to negotiations, just as it has to the threat of growing US output for the last two years.

Brent futures, which had topped $110 per barrel for the first time in November on Friday as the prospects of an Iranian deal appeared to recede, have retreated for now. But hopes for a sustained period of lower oil prices may need to wait.

Goldman Sachs analysts told clients on Monday morning: “We view the immediate impact of the agreement on the level of Iranian crude oil supply to the international market as limited.”