The Obama administration on Monday implemented new air cargo security rules as part of an effort to prevent a repeat of last month's attempt to send bombs to the U.S. on board cargo planes. Under the new rules, toner and ink cartridges that weigh one pound or more will not be allowed to be brought on board passenger flights as well as certain cargo flights.

The White House is concerned that large toner and ink cartridges like the ones used in office printers and copiers could be used to hide explosives, just like they were used in last month's cargo bomb plot. Broader new air cargo security rules were also put into effect on Monday. Those rules call for airlines and cargo companies to inspect any international mail packages and any other type of high-risk package placed on board a flight bound for the U.S.

Homeland security officials refused to define what constituted a high-risk package, though industry officials said the rules most likely applied to shipments from countries where terrorists are known to operate as well as packages sent by an unknown shipper.

Meanwhile, Somalia has been added to the list of countries that the U.S. has banned air cargo shipments from. More security rules could be coming in the future, including rules that require airlines and cargo planes to provide detailed cargo manifests before cargo planes take off for the U.S.