U.S. President Barack Obama signed an executive order implementing parts of the Iran Threat Reduction and Syria Human Rights Act of 2012.
Tommy Vietor, a spokesman for the National Security Council, said the measure broadens certain aspects of sanctions on Iranian authorities while tightening sanctions targeting the country's energy sector.
"It builds on the sanctions that have been imposed on the Iranian government, and provides for additional sanctions on activities related to Iran's energy and financial sectors, proliferation of weapons of mass destruction, support for terrorism and activities related to human rights abuses by Iran and Syria, among other things," he said in a statement.
Obama signed the act into law in August. His executive order created the foundation for the enforcement of sanctions. Vietor said Iran may face additional "consequences" should it continue "its defiance."
Washington and its European allies last month accused Iran of supporting the Syrian military amid growing frustration with Tehran's role in the international community.
U.S. Ambassador to the United Nations Susan Rice had said Iranian support for the "murderous" regime in Damascus was "of particular concern."