Story highlights Iran "unmoved" by Trump's threat; one official cites the need for self-defense

Administration "officially putting Iran on notice," Flynn said Wednesday

(CNN) The White House is expected to impose additional sanctions on Iranian entities under existing executive orders that predate President Donald Trump, according to sources familiar with the move.

The additional sanctions are in response to Iran's ballistic missile test on Sunday. They are similar to actions taken by former President Barack Obama after Iran's previous ballistic missile tests.

In a letter to Trump Thursday, a bipartisan group of senators said, "Iranian leaders must feel sufficient pressure to cease deeply destabilizing activities, from sponsoring terrorist groups to continued testing of ballistic missiles."

"Full enforcement of existing sanctions and the imposition of additional sanctions on Iran for its ballistic missile program are necessary," the letter said.

Read More