The European Union is poised to ban imports of gas from Iran as part of a set of new measures to ratchet up pressure on the republic over its nuclear programme.
Diplomats from EU member states have started preparing a package of sanctions against Iran.
It is likely they will be adopted at a meeting of foreign ministers on 15 October in Luxembourg.
European governments and the United States are searching for fresh ways to pressure Tehran into scaling back its nuclear programme.
Tehran denies its work has any military intentions. But the value of the rial has plunged against the value of the dollar in recent days sparking unrest on the streets of the capital on Wednesday.
The United States has banned US firms from investing in Iranian oil and gas and from trading with Iran since 1995.
Last December it adopted steps that prompted buyers in Japan, South Korea and India to cut oil purchases from Iran. In July the US announced sanctions against foreign banks helping Tehran sell oil.
The European Union imposed an embargo on Iranian oil this year, after banning the creation of joint ventures with enterprises in Iran engaged in the oil and natural gas industries in 2010.