Homeland Security Secretary John Kelly Tuesday called marijuana a “gateway drug” and vowed his agency will uphold federal laws against its possession, a sterner message than he delivered on the topic just last week.

“Let me be clear about marijuana. It is a potentially dangerous gateway drug that frequently leads to the use of harder drugs,” Kelly said during a speech about his agency's mission at George Washington University in Washington, D.C.

“Its use and possession is against federal law and until the law is changed by the United States Congress, we in DHS, along with the rest of the federal government, are sworn to uphold all the laws that are on the books,” he added.

Kelly made headlines on Sunday when he told NBC News’ Chuck Todd that “marijuana is not a factor in the drug war” during an interview on “Meet The Press.”

That was a noticeably softer tone than other members of President Donald Trump’s administration have taken, especially Attorney General Jeff Sessions, an open opponent of legal weed. And Kelly seemed to go out of his way Tuesday to say marijuana is not something the administration takes lightly.

“When marijuana is found at aviation checkpoints and baggage screening, TSA personnel will also take appropriate action,” Kelly said. "Finally, ICE will continue to use marijuana possession, distribution and convictions as essential elements as they build their deportation, removal apprehension packages for targeted operations against illegal aliens.”

Kelly warned on Sunday that the White House is changing how they weigh crimes by undocumented immigrants. Driving under the influence, Kelly said, could now start the process of deporting those in the country illegally.