The US financial and economic sanctions against Iran violate the charter of the International Monetary Fund (IMF), which demands free trade between all member states, Kostin told Russian TV channel RBK on Friday.
Kostin criticized the US for manipulating its currency on the international markets, stressing that the move also breaches the principles of the IMF.
US President Barack Obama authorized a law on New Year's Eve imposing fresh sanctions on financial institutions that deal with the Central Bank of Iran, Tehran's main clearing house for oil payments.
The extra US sanctions aim to squeeze Iran's oil sales, most of which are processed by the CBI, although many even in the West believe that the move would prove futile.
During the last two years, Iran has been replacing dollar with other currencies in its trade with the outside world.
In May, the International Monetary Fund (IMF) opposed a call by a New York-based anti-Iran group to halt business with the Central Bank of Iran.
The anti-Iran group whose founders include current and former administration officials has sent a letter to IMF Managing-Director Christine Lagarde criticizing the IMF's relationship with Iran.
In reply, the IMF said on Tuesday that its relationship with the Central Bank of Iran is based on its constitution, noting that Iran's membership does not contravene US or EU sanctions on Tehran.
"According to our constitution... the IMF's holdings of each member's currency are maintained with the central bank of the relevant member, including Iran. There is nothing in the EU or US sanctions regimes that is inconsistent with these arrangements," IMF spokesman William Murray said.
Earlier in April, Lagarde praised Iranian President Mahmoud Ahmadinejad's subsidy-cuts plan, and described it as a brave move which should be followed by other countries.
Lagarde made the remarks, addressing a joint meeting of the World Bank and the IMF.
She referred to Iran's measures in reforming its subsidiary system in the past two years as exceptional, and called on other world countries to follow the role model of Iran in carrying out reforms.