The United States has imposed sanctions on two Singapore-based companies over their dealings with Iran, the Southeast Asian city-state's Ministry of Foreign Affairs said on Friday.

The ministry said the action against the two Singapore firms, Mid Oil Asia Pte Ltd and Singa Tankers Pte Ltd, was based on U.S. rules that were "above and beyond the sanctions imposed by the United Nations Security Council, which are mandatory on all U.N. members."

"We are also not in a position to enforce the laws of other countries," the ministry added in a statement.

"However, given the importance of the U.S. in the world economy, we expect companies with dealings with countries subject to unilateral U.S. sanctions will take notice of these and other prior cases and make their own calculations and decisions based on how this might impact on their own commercial interests," it added.

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