Security tightened on US flights

The new security measures are to be required at airports in Europe, Africa and the Middle East that have direct flights, US officials told Reuters news agency.

The Department of Homeland Security said on Wednesday "enhanced security measures" would be implemented in the next few days at "certain overseas airports with direct flights into the United States."

"We are sharing recent and relevant information with our foreign allies and are consulting the aviation industry," DHS Secretary Jeh Johnson said in a statement.

It did not specify which airports or what countries would be affected, nor did it say what triggered the extra precautions, though the Associated Press reported that intelligence officials are concerned about a new al-Qaeda effort to create a bomb that would go undetected through airport security.

In the past officials have raised concerns about non-metallic explosives being surgically implanted inside a traveler's body, designed to be undetectable in pat-downs or metal detectors.

New threats from Syria and Yemen

A US official told Reuters some of the new measures would involve additional inspections of passengers' shoes and property. Washington has legal authority to enforce new security requirements on foreign governments or airports because the flights go directly to the United States.

The spiraling conflicts in the Middle East are also thought to be providing new threats. Bombmakers from the Nusra Front, an al Qaeda affiliate in Syria, and Yemen-based Al Qaeda in the Arabian Peninsula (AQAP), are believed to be cooperating to develop explosives that could avoid detection by current airport screening systems.

On Sunday, US President Barack Obama warned that "battle-hardened" European jihadists returning from Syria and Iraq threaten the United States.

These combatants "have a European passport. They don't need visas to get into the United States," he told the program "This Week."

"We're targeting certain airports abroad... based on real time intelligence," a DHS official told AFP news agency. The new measures would be designed in a way to avoid creating major hassles for travelers, without signaling to potential terrorists what those steps would be, officials said.

"Information about specific enhancements is sensitive as we do not wish to divulge information about specific layers of security to those who would do harm," said a second DHS official, who asked not to be named.

bk/jr (Reuters, AP, AFP)