The White House moved to enforce tightened sanctions against Iran on Monday because of the country’s suspect nuclear program, freezing all property of the Central Bank of Iran, other Iranian financial institutions and the Iranian government in the United States.

The actions were announced in an executive order signed by President Obama that started the enforcement process for a tough measure he signed into law at the end of 2011. If fully carried out, that measure could isolate Iran’s central bank and effectively choke off the sale of Iranian oil by obstructing the means of payment. Most of the revenue for oil sales by Iran, one of the world’s biggest oil exporters, is processed by its central bank.