Americans awoke on a Monday after the Thanksgiving holidays to learn that a series of terrorist threats had been uncovered by American and British authorities.

According to officials in the U.K., aspiring terrorists were planning a Christmas “spectacular” coordinated attack targeting five commercial jets over the holiday. The U.K. Express reported on Monday that British officials have conceded that an attack of some kind is all but “inevitable,” and authorities are taking precautions such as banning nearly all carry-on bags at airports.

The plot, which has been known about for the past two months, is thought to involve Islamists smuggling bombs on to planes bound for major European destinations before Christmas.

The well-placed security insider said talks had been held about how to deal with it, with suggestions made to ban hand luggage.

A source said: “High level negotiations are continuing at Governmental level but at the moment there has been little done to respond.

“There is paralysis because of the difficulty of banning hand luggage which is one of the strongest weapons we have against the new threats.”

The most frightening element of this plot is the likelihood that the conspirators are seeking to execute attacks on a European cities. “The most likely scenario is a plane heading towards a major European capital,” terrorism expert Dr. Sally Leivesley told The Express. “There is likely to have been dry runs already with terrorists testing airport security.”

Officials concede that this threat is aimed exclusively at Europe because American airport security has been increased to the point that an attack of this scale is difficult to achieve in the United States. Federal officials warned, however, that militants aligned with the Islamic State are urging low-tech attacks against the U.S. military inside American borders.

Via ABC News:

In a joint intelligence bulletin issued overnight by the FBI with the Department of Homeland Security, officials strongly urged those who serve in uniform to scrub their social media accounts of anything that might bring unwanted attention from “violent extremists” or would help the extremists learn individual service members’ identities.

“The FBI and DHS recommend that current and former members of the military review their online social media accounts for any information that might serve to attract the attention of ISIL [ISIS] and its supporters,” the federal bulletin sent to law enforcement agencies said, advising that troops “routinely exercise operational security in their interactions online.”

Officials said they fear copycat attacks based on what happened in Canada last month, when two uniformed Canadian soldiers were killed in two separate incidents by young men who claimed they were ISIS followers.

“The FBI recently received reporting indicating individuals overseas are spotting and assessing like-minded individuals who are willing and capable of conducting attacks against current and former U.S.-based members of the United States military,” that bulletin continued.

Over the weekend, an American oil worker stationed in Egypt’s Sinai Peninsula was allegedly killed by the Islamic State-aligned group Ansar Beit al-Maqdis. The murder of William Henderson, a 58-year-old Texas native, has not yet been confirmed by the American embassy in Egypt.