The US on Tuesday slapped sanctions against two banks for dealing with Iranian financial institutions on Washington's designated don't-touch list.
The Obama administration also announced sanctions against any entity buying petrochemicals from Iran, which is its second largest import after crude.
And there is more coming as US congress is to pass on Wednesday a legislation adding sanctions on any country or company that mines uranium for Iran or sells it oil tankers.
"With these actions, we are once again reaffirming our commitment to hold the Iranian government accountable for its actions," said President Barack Obama in a statement.
The two banks sanctioned Tuesday - essentially punished by being shut out of the US financial system - were China's Bank of Kunlun and Iraq's Elaf Islamic Bank.
Bank of Kunlun was providing financial services worth millions of dollars to more than six Iranian banks designated for links to terrorism and WMD production, said US treasury.
And Elaf Islamic Bank dealt with the Export Development Bank of Iran designated by the US in October 2008 and by the European Union in July 2010.
The two banks were the first to be slapped with sanctions under a US law passed and signed in July 2010, and are intended to have a salutary effect on others.
"The message to banks worldwide should be clear: If you provide financial services to designated Iranian banks, if you process significant financial transactions for those banks, you will face US sanctions," said senior treasury official David Cohen.