Washington is renewing its focus on international aviation security as evidence increasingly points to the possibility that a bomb destroyed a Russian passenger airliner over Egypt's Sinai Peninsula, killing all 224 people aboard the jet.
Although much of the tragedy remains shrouded in mystery, a clue emerged from the doomed Airbus' cockpit voice recorder that could point to a bomb.
"A noise was heard in the last second of the CVR recording," said Egyptian lead investigator Ayman El-Muqadem.
While further analysis continues, a claim of responsibility was repeated on social media.
"With God's help, the fighters of the Caliphate managed to down the Russian plane over Sinai," said a message in Arabic purportedly from the Islamic State (IS) group.
U.S. lawmakers are reaching their own conclusions.
"I am almost ready to conclude that it was either ISIS or an ISIS affiliate," said Republican Congressman Peter King, using and alternate acronym for the group. He spoke on ABC's This Week program.
"ISIS has now fully eclipsed al-Qaida as the gravest terrorist threat in the world," said Democratic Congressman Adam Schiff, speaking on the same program.
Schiff, who is the top Democrat on the House Intelligence Committee, said IS appears to have discovered a vulnerability in international aviation that requires urgent attention.
"ISIS may have concluded that the best way to defeat airport defenses is to go around them with the help of someone on the inside. And if that is the case, there are at least a dozen airports in the region and beyond that are vulnerable to the same kind of approach," he said.
Schiff added that European and U.S. international carriers could be at particular risk. At major U.S. airports, screening procedures have been boosted in recent days.
Meanwhile, Russia and Britain have suspended flights to Egypt as the probe of the Metrojet disaster continues.
Vocabulary
shroud：覆盖
cockpit：驾驶员座舱