U.S. President Barack Obama promised tough action on Tuesday against firms violating sanctions against Iran, AFP reported.

Obama made the comments during a joint press conference in Washington with visiting French President Francois Hollande.

Last week, a delegation of French business figures visited Tehran, hoping to explore ways of resuming trade with Iran after a landmark nuclear deal reached with the major powers in November gave Iran limited relief from crippling U.S. and EU sanctions.

That visit elicited criticism from U.S. Secretary of State John Kerry, who told his French counterpart Laurent Fabius that the trip, even though organized through the private sector, was “not helpful” in sending the message that “it is not business as usual” with Iran.

France’s Finance Minister Pierre Moscovici responded by saying the 116-person delegation is “a bet” on the future and not “business as usual.”

On Tuesday, reported AFP, Obama had tough words for anyone hoping the now looser embargo would leave an open door.

“Businesses may be exploring: ‘Are there some possibilities to get in sooner rather than later if and when there is an actual agreement to be had?’,” Obama said, standing alongside Hollande.

“But I can tell you that they do so at their own peril right now. Because we will come down on them like a ton of bricks,” he declared.

Hollande said he does not control French corporations but made it clear that sanctions on Iran would not be dismantled until a final deal on Iran’s nuclear program had been reached.

“So companies just make their decisions when it comes to traveling, but I certainly let them know that sanctions were in force and would remain in force,” Hollande said.

“Sanctions will only be lifted if and when there is definite agreement,” Hollande said, insisting that Iran must have “renounced the nuclear weapon, fully and comprehensively.”

Many French firms have longstanding commercial arrangements with Iran despite political tensions and Paris’ steadfast opposition to its nuclear drive, which the Islamic Regime insists is peaceful.

Obama has welcomed the interim nuclear deal as a victory for his muscular diplomacy, but he faces domestic pressure not to move too quickly on the easing of sanctions.

Some U.S. lawmakers have been pushing for stronger measures, despite warnings from the White House that this could scupper the negotiations and lead to a military confrontation with Iran.

“We don’t want new sanctions, because the ones we have in place are already squeezing Iran and brought them to the table,” Obama told the news conference, according to AFP.

“But we also want to send a message to the Iranians … that the sanctions regime not only will stay in place, but will likely be tightened in the event these talks fail,” he said.