Handout photo satellite image of the Russian airplane crash site on the Sinai Peninsula.

Communications between ISIS leaders in Raqqa, Syria, and persons in the Sinai Peninsula included boasts about the downing of a Russian passenger jet over the area, NBC reported on Friday, citing unidentified U.S. officials.

“They were clearly celebrating,” NBC Nightly News quoted a U.S. official as saying. The “chatter” included a boast of taking down the plane on Saturday and how it was done.

The U.S. intelligence community intercepted a message from a Sinai group affiliated with ISIS that warned of “something big in the area” before the jet crash.

U.S. steps up screening of flights

The U.S. said Friday it was stepping up security screenings of U.S.-bound flights from some Middle East airports as a precaution after the crash of the Russian airliner in Egypt.

Homeland Security Secretary Jeh Johnson said the U.S. 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.”

There is growing evidence that the plane that crashed Saturday in the Sinai, killing all 224 people, was brought down by an explosion.

Sources close to the investigation told AFP that information from the airliner’s flight data and voice recorders “strongly favors” the theory that a bomb exploded on board the Airbus A321.

Russia suspends Egypt flights

Moscow suspended passenger flights to Egypt, but has said it is premature to reach conclusions that the flight was attacked.

However President Vladimir Putin agreed with Egyptian President Abdel Fattah al-Sisi to bolster coordination to secure Russian flights and resume them as soon as possible.

Sisi called Putin and they agreed “to bolster cooperation between the two countries’ relevant agencies to ensure the safety of Russian tourists and strengthen security measures for Russian planes,” a statement said.

International security warnings

Following international security warnings in the wake of the crash, Denmark urged its citizens on Friday to avoid Egypt’s southern Sinai Peninsula, including the Sharm el-Sheikh resort.

The foreign ministry said the advice was based on an assessment of aviation safety made after fresh information was received on Friday, without going into further details.

The Danish ministry said on its website it now advised “against non-essential journeys to the southern part of the Sinai Peninsula, including Sharm el-Sheikh”.

In this photo made available Monday, Nov. 2, 2015, and provided by Russian Emergency Situations Ministry, Egyptian Military on cars approach a plane’s tail at the wreckage.

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