On Sunday UBS corroborated a report in the SonntagsZeitung newspaper, but stressed that implementation of the decision had already begun last autumn.
All existing business with Iranian customers – barring those in exile – would be wound down, although it was unclear how long this process would take.
Company spokesman Serge Steiner added that the measure was the result of an internal risk assessment, which took into account that Iran was tagged as one of the countries belonging to the so-called axis of evil.
In the end, it was also a question of revenue and expense, said Steiner, and the burden of regulatory compliance in countries like Iran was simply too heavy.
However, he insisted that the bank’s decision had nothing to do with the current crisis that has erupted over Iran’s recent resumption of its nuclear programme in the face of international opposition.
Switzerland’s second largest bank, Credit Suisse, admitted that it too was watching the situation in Iran very closely.
Meanwhile, Iran has denied that it is shifting its foreign currency reserves out of Europe in a pre-emptive move ahead of possible United Nations sanctions.
The UN’s International Atomic Energy Agency is due to meet in February to discuss whether Tehran should be referred to the UN Security Council.
The latter has the power to impose international sanctions.