The US has extended an air cargo ban to cover Somalia as well as Yemen and banned ink and toner cartridges from passenger flights, in the wake of last month's failed bomb plot.
High risk cargo will receive extra screening and parcels must be certified to have come via established shippers.
The strictures come after bombs hidden in cartridges were intercepted on route from Yemen to the US in cargo planes.
Homeland Security boss Janet Napolitano said US security was the top priority.
"The threats of terrorism we face are serious and evolving, and these security measures reflect our commitment to using current intelligence to stay ahead of adversaries-working closely with our international, federal, state, local and private sector partners every step of the way," she said.
Ms Napolitano said US Transportation Security Administration officials had met in Yemen with officials there, in an effort to enhance Yemeni security enhancements so the cargo ban eventually could be lifted.
The printer cartridge ban affects cartridges over 16 ounces (453g).
The US had already halted all cargo from Yemen. On Monday, Ms Napolitano announced the ban would be extended to include Somalia, a haven for al-Qaeda-affiliated Islamist militants.