The order, issued Tuesday, would allow the government to punish any individuals who either violate current sanctions against the two countries or help facilitate such an evasion by others.
The order "provides Treasury additional means to impose serious consequences on foreign persons who seek to evade our sanctions and undermine international efforts to bring pressure to bear on the Iranian and Syrian regimes," said David Cohen, the Treasury's undersecretary for terrorism and financial intelligence. "Whoever tries to evade our sanctions does so at the expense of the people of Syria and Iran, and they will be held accountable."
Once the Treasury identifies someone who is trying to avert the sanctions, anyone under U.S. jurisdiction would be prohibited from doing business with them. The Treasury said the new order helps ensure that Americans do not accidentally undercut the sanctions.
Obama notified Congress of the move in letters sent to the Speaker of the House and the President of the Senate.
The move marks the latest attempt by the White House to put pressure on the two nations. In February, another executive order levied new sanctions on Iran and its central bank.
Under that order, any Iranian assets held by U.S. citizens or companies were effectively frozen, and any transactions conducted by U.S. citizens with Iranian entities would be seized or frozen.
The White House is putting pressure on Iran to halt its nuclear development program and bearing down on Syria because of its deadly crackdown on political protesters.