Don't bring dead phones or laptops to those overseas airports for flights heading to the USA.
Department of Homeland Security officials warned last week that security would tighten at airports where flights head directly to the USA but without providing much detail about how the scrutiny would change.
But security officials said Sunday that the attention is focused on explosives that could be disguised as electronic devices.
The Transportation Security Administration issued a statement Sunday saying that as part of its routine screening at the overseas airports with direct flights, checkpoint officers may ask owners to turn on devices including cellphones.
Devices that can't be turned on won't be permitted on flights, TSA said. Travelers also may undergo additional screening such as pat-downs.
"In this instance, we felt that it was important to crank it up some at the last point-of-departure airports," Jeh Johnson, secretary of homeland security, said on NBC's Meet the Press on Sunday. "And we'll continually evaluate the situation."
After earlier threats involving explosives in shoes and liquids, most travelers were asked to remove their shoes for X-ray at checkpoints and larger containers of liquids were prohibited on flights.
Johnson said the latest change is an attempt to anticipate the next attack rather than simply react to the last one. But he said there is no reason to overreact or speculate about it.
"We know that there remains a terrorist threat to the United States," Johnson said. "And aviation security is a large part of that."
The changes announced Wednesday met little public criticism. Rep. Michael McCaul, R-Texas, chairman of the House Homeland Security Committee, said the threat from al-Qaeda and other groups is constantly evolving and targets aviation.
"Aviation security is only as good as the weakest link, and it is essential that our allies, the airline industry and airports that serve as last points of departure to the U.S. strengthen and then maintain enhanced security measures," McCaul said.