The United States is vamping up its efforts to stop terrorists from sneaking themselves, or perhaps a dirty bomb (search), into America by ship.

Thursday is the deadline for new terrorist security regulations, which mandate that every foreign-flagged vessel that sails into a U.S. port will have to comply with various security rules. The rules are part of a global effort, which include boarding every ship before docking and screening huge container ships.

"It's pretty clear, given their focus on international transportation ... those are current themes in threat reporting … thousands of vessels on the oceans could transfer terrorists or terrorist weapons," Homeland Security Tom Ridge (search) told FOX News in an interview.

Ridge said he's confident the new rules will clamp down on the possibility of terrorists exploiting the high seas.

About 6 million huge metal shipping containers come into the country every year and even though only about 6 percent of them are actually X-rayed, Ridge said that's sufficient because of the many other redundant safety measures in place.

One study estimates only about one-tenth of all foreign ports will be ready by Thursday's deadline but Ridge isn't worried.

Officials say Al Qaeda has already targeted shipping containers (search).

One operative was arrested last year for trying to bribe his way into using one going to Port Newark in New Jersey. Al Qaeda documents exposed a plot to send radioactive material into a U.S. port in a container holding sesame seeds. And two years ago, Italian authorities nabbed a suspected Al Qaeda member who was sealed inside a container with food and water.

Click on the video box at the top of this story to watch a report by Fox News' Eric Shawn.