According to the new rules, all US-bound passengers aboard international flights must undergo a "thorough pat-down" at boarding gates, focused on the upper legs and torso.
All carry-on baggage must be inspected, the rules say.
In the final hour before landing, all passengers in the flights must remain seated. During that time, they may not have access to their carry-on baggage or hold personal items on their laps.
While over US airspace, flight crews may not make any announcements to passengers concerning the flight path or the airplane's position over cities or landmarks, the new rules said.
Earlier in the day, Homeland Security Secretary Janet Napolitano said passengers flying from international locations to US destinations may notice additional security measures in place.
"These measures are designed to be unpredictable, so passengers should not expect to see the same thing everywhere. Due to the busy holiday travel season, both domestic and international travellers should allot extra time for check-in," he said in a statement.
The new restrictions follow Christmas Day's foiled attempt by a Nigerian terrorist suspect to explode Northwest Flight 253 from Amsterdam as it was landing in Detroit with about 300 people on board.
Anecdotal reports described how screeners have required a mother travelling with a baby to provide samples of each and every bottle of milk she was carrying.
Another man told CNN that screeners had taken apart his laptop case.
There were reports that passengers would now be required to remain seated for an hour before landing, with no access to toilets or luggage stored above the seats. Passengers may not be able to have pillows or blankets in the hour before landing.
In addition, there were reports that the GPS systems displayed on viewing screens in passenger planes are to be shut off to deny passengers orientation about the progress or position of the plane.
Governments have increasingly tightened security measures since the 2001 terrorist attacks on the US, when hijackers commandeered four passenger planes and killed nearly 3,000 people.
Since terrorist Richard Reid, a Briton, tried to blow up an American Airlines plane in December 2001 with PETN explosives molded into his shoes, travellers must remove their shoes for examination.
Since the 2006 foiled attempt in London to blow up seven intercontinental airliners with liquid explosives, travellers are limited in what sort and amount of liquids they can carry on board and can no longer carry their own food or water.
