WASHINGTON • Islamic State in Iraq and Syria (ISIS) leaders in Syria and persons in the Sinai Peninsula boasted about the downing of a Russian passenger jet over the area after last week's deadly crash that killed 224 people, according to communications intercepted by the United States and British intelligence services, NBC has reported.

"They were clearly celebrating," NBC Nightly News on Friday quoted an unidentified US official as saying. The "chatter" included a boast of taking down the plane last Saturday and how it was done.

Amid growing evidence that the plane was brought down by a bomb, French TV station France 2 said on its website that the sound of an explosion could be heard on the black boxes recovered from the plane, according to an investigator who had access to them. The investigator ruled out engine failure, it added.

Egypt yesterday expressed frustration that foreign intelligence about the cause of the crash had not been passed on to Cairo.

"The information we have heard about has not been shared with Egyptian security agencies in detail," said Foreign Minister Sameh Shoukry. "We were expecting that the technical information would be provided to us."

Amid heightened perceptions of a terrorist threat, the US said on Friday it was stepping up security screenings of US-bound flights from some Middle East airports as a precaution.

Homeland Security Secretary Jeh Johnson said the US also would review its assessments of certain foreign airports and offer them help with security, as well as take other measures, "both seen and unseen".

Meanwhile, Russia has disclosed that nearly 80,000 Russians are currently vacationing in Egypt. But there will be no emergency evacuation, a day after Russian President Vladimir Putin ordered flights to the Sharm el-Sheikh halted.

"Tourists will be returning from Egypt to Russia when they planned to," said Deputy Prime Minister Arkady Dvorkovich, who is in a charge of a task force established to oversee the return of tourists.

Adding to the growing concerns over tourist safety in Egypt, it has emerged that a British passenger jet came close to being hit by a rocket fired by Egypt's military during a military exercise as it came in to land at Sharm el-Sheikh in August, British media reported yesterday, although the British government said it concluded the incident was not a deliberate attack.

REUTERS, AGENCE FRANCE-PRESSE