A pro-ISIS Twitter account has issued a threat of a terrorist attack over the July 4 holiday weekend.
The information was revealed by the SITE Intelligence Group, an organization which tracks jihadist groups, according to the Daily Mail.
The account alleged that planes “flying from Heathrow [Airport] to the US” would be attacked, and also warned that “there will be a device placed in either Heathrow, LAX or JFK airports.” LAX and JFK refer to airports in Los Angeles and New York.
Rita Katz is the head of the SITE group and has tracked Islamist extremist groups for two decades. She has been recognized by the FBI for her “outstanding assistance to the FBI in connection with its investigative efforts.”
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The FBI says it has no evidence that attacks are planned over the coming weekend.
“However, law enforcement and members of the public must remain vigilant. ... The FBI asks members of the public to maintain awareness of their surroundings and to report any suspicious activity to law enforcement,” an FBI spokeswoman said in a statement.
The July 4 weekend is one of the busiest traveling weekends of the year. Estimates suggest up to 43 million people will be on the move in the lead-up to Independence Day.
The warning comes just days after 43 people were killed in an ISIS attack on an airport in Istanbul, Turkey. Three men attacked people at the airport with rifles before setting off suicide bombs.
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Michael McCaul, the chairman of the House Committee on Homeland Security, told CNN that the Istanbul attack was masterminded by Akhmed Chatayev, an Islamic extremist from Russia with ties to ISIS.
"He's … probably the no. 1 enemy in the Northern Caucasus region of Russia," McCaul said to CNN. "He’s traveled to Syria on many occasions and became one of the top lieutenants for the minister of war for ISIS operations."
The U.S. Treasury added Chatayev to its list of terrorists last year, saying that he was planning attacks on both the United States and Turkey.
McCaul alleged he obtained this information from Turkish intelligence.
Police in Istanbul say 80 people remain in the hospital after the attack.