President Barack Obama says his administration is fully enforcing existing sanctions on Iran.

"We have taken various steps just over the last six, seven weeks, to identify companies we felt were violating those sanctions and have been very clear to the Iranians that there's not going to be any letup."

In a joint news conference with France's president, President Obama issued a strong warning to lawmakers today against new sanctions on Iran.  He said they could complicate sensitive international negotiations aimed at ending Iran's nuclear program.  

Some U.S. lawmakers are pushing for additional sanctions while talks are ongoing.