Kaplan, a US-owned education provider in the UK, is refusing students who are residents of Iran enrolment in science, technology, engineering and mathematics (Stem) subjects as well as any of its post-graduate courses, citing US sanctions.

Applications for more than a dozen Iranians students have been withdrawn since autumn 2013 because the company felt it had to comply with the US regulations and sanctions policy regarding the country.

Critics say sanctions were put in place to punish Iranian authorities, not ordinary people, and that such interpretations were based on a misreading of the policy.

Iranian students studying in Britain's public universities can generally take such courses.

An internal memo aimed at clarifying Kaplan's position on Iranian students, seen by the Guardian, states that the company can enrol students who are resident in Iran only on undergraduate non-Stem courses.

"US companies are generally prohibited from exporting services to or importing services from Iran," read the memo. "In practice, this means there are some limitations on the students Kaplan can recruit, especially those who are resident in Iran. We can usually enrol Iranian students who are domiciled outside Iran, subject to certain restrictions on how the student pays for their course."

At least one Iranian student who studied in the UK through Kaplan was refused a certificate at the end of her studies after the company updated its Iran policy.

Ali Shafie, of UKstudy.com, a company that has assisted Iranian students into UK education, said Kaplan's policy was discriminatory.

"Kaplan seems to have arbitrarily decided to ban Iranians from enjoying the same pathway courses at UK universities that all other nationalities currently enjoy," he told the Guardian. "As they are providing on-campus courses at UK government-owned universities, they have a responsibility to not discriminate on the basis of nationality when offering places."

Shafie said UK universities must comply with the academic technology approval scheme (Atas), which requires clearance for certain sensitive courses. He believes that is why Kaplan could not make a separate parallel decision.

"Iranians already face such difficulties in obtaining visas to study in the UK and also have to deal with a wildly fluctuating exchange rate," he said. "They do not deserve to have to also deal with this type of discrimination on the basis of their nationality."

A Kaplan spokesperson said: "Operating in compliance with the limitations of the US sanctions against Iran, Kaplan, as a US-owned company, is committed to recruiting international students with a diverse mix of nationalities including those from Iran.

"Kaplan keeps the US sanctions under constant review and ideally we would want to be able to offer our pathways courses to all students, regardless of residence."

Earlier in June, Coursera, a giant provider of online courses, announced it was restoring access in Iran to the majority of its courses, excluding science, technology, engineering and maths.

"Sanctions still prohibit educational institutions and organisations from offering certain subjects, including those in advanced Stem [subjects]. To comply, we have identified those specific courses and will be blocking enrolment to learners coming from Iranian IP addresses," Coursera said in a statement published on its website.

Despite such policies, Iranian students can generally study the same types of courses in American universities on US soil.

US and EU sanctions on Iran over its nuclear programme have taken a toll on ordinary people in recent years. Patients in Iran, such as those with cancer, have faced immense difficulties in obtaining medicines because of a shortage caused by sanctions. Although medicine is not directly targeted by sanctions, blanket banking restrictions mean Iranian companies have little or no way to pay western sellers.

This year a group of Iranians in the UK complained that they had been told their bank accounts had to be closed because of sanctions. The group, which included a nine-year-old girl, have since challenged three high-street banks in the courts, claiming they have been subjected to racial discrimination.

In Norway, several Iranian students claimed a few weeks ago that the authorities were asking them to leave the country over fears they could transfer sensitive technology to Iran, Iran's state-run Press TV reported.

Hamideh Kaffash, one of the students, said she could not continue her education at the Norwegian University of Science and Technology although she was working on an environmental project that had nothing to do with sensitive technology.