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(L/R): Head of Dutch Military Intelligence and Security Service Onno Eichelsheim, Minister of Defence Ank Bijleveld and British ambassador Peter Wilson attend a press conference of the Dutch Military Intelligence and Security Service (MIVD) at The Hague, The Netherlands, on October 4, 2018. - Dutch intelligence thwarted a Russian cyber attack targeting the global chemical weapons watchdog in April and expelled four Russian agents, the government said. The Russians set up a car full of electronic equipment in the car park of a hotel next to the Organisation for the Prohibition for Chemical Weapons in The Hague in a bid to hack its computer system, it said. (Photo by Bart Maat / ANP / AFP) / Netherlands OUT        (Photo credit should read BART MAAT/AFP/Getty Images)
BART MAAT/AFP/Getty Images
(L/R): Head of Dutch Military Intelligence and Security Service Onno Eichelsheim, Minister of Defence Ank Bijleveld and British ambassador Peter Wilson attend a press conference of the Dutch Military Intelligence and Security Service (MIVD) at The Hague, The Netherlands, on October 4, 2018. - Dutch intelligence thwarted a Russian cyber attack targeting the global chemical weapons watchdog in April and expelled four Russian agents, the government said. The Russians set up a car full of electronic equipment in the car park of a hotel next to the Organisation for the Prohibition for Chemical Weapons in The Hague in a bid to hack its computer system, it said. (Photo by Bart Maat / ANP / AFP) / Netherlands OUT (Photo credit should read BART MAAT/AFP/Getty Images)
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Bowtie TV
The UK will expel 23 Russian diplomats from the country after concluding that the Russian state is responsible for the attempted murder of former Russian agent, Sergei Skripal and his daughter Yulia in Salisbury on March 4th. They will have one week to leave. "For those who seek to do us harm, my message is simple. You are not welcome here."
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SALISBURY, ENGLAND - JULY 05:  A police officer stands by a cordon in place at Queen Elizabeth Gardens in Salisbury after a major incident was declared when a man and woman were exposed to the Novichok nerve agent on July 5, 2018 in Salisbury, England. The couple, named locally as Dawn Sturgess 44, and Charlie Rowley, 45 were taken to Salisbury District Hospital on Saturday and remain there in a critical condition. In March Russian former spy Sergei Skripal and his 33-year-old daughter Yulia were poisoned with the Russian-made Novichok in the town of Salisbury. British Prime Minister Theresa May has accused Russia of being behind the attack on the former spy and his daughter, expelling 23 Russian diplomats in retaliation. (Photo by Jack Taylor/Getty Images)
Jack Taylor/Getty Images
SALISBURY, ENGLAND - JULY 05: A police officer stands by a cordon in place at Queen Elizabeth Gardens in Salisbury after a major incident was declared when a man and woman were exposed to the Novichok nerve agent on July 5, 2018 in Salisbury, England. The couple, named locally as Dawn Sturgess 44, and Charlie Rowley, 45 were taken to Salisbury District Hospital on Saturday and remain there in a critical condition. In March Russian former spy Sergei Skripal and his 33-year-old daughter Yulia were poisoned with the Russian-made Novichok in the town of Salisbury. British Prime Minister Theresa May has accused Russia of being behind the attack on the former spy and his daughter, expelling 23 Russian diplomats in retaliation. (Photo by Jack Taylor/Getty Images)
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Russian President Vladimir Putin delivers a speech during a meeting with Russian athletes and team members, who will take part in the upcoming 2018 Pyeongchang Winter Olympic Games, at the Novo-Ogaryovo state residence outside Moscow on January 31, 2018. / AFP PHOTO / SPUTNIK / Alexey NIKOLSKYALEXEY NIKOLSKY/AFP/Getty Images
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(CNN) —  

A U.S. official told CNN Thursday that Russian fighter jets turned off their transponders as they flew into Syria in an apparent attempt to avoid detection. The official said the fighters flew very close to a transport plane that had its transponder on and functioning.

U.S. satellites rapidly saw that the aircraft were there, according to the official.

The assessment over the weekend was that the fighter jets were on their way. The same official said the Russians have begun flying drones around the coastal city of Latakia.

Russia launches drones in Syria

With no ISIS fighters in the area, the move raises serious questions about the Russians’ intentions with their military buildup, which the U.S. has questioned the purpose of and watched with wariness. The action points to a higher likelihood that the Russian plan is to prop up Syrian President Bashar al-Assad rather than fight the terror group.

Is Russia preparing to move troops to 2 new Syria bases?

The U.S. has its own effort underway to defeat ISIS but has also said that Assad must go.

Asked about what the U.S. can do about the situation, Defense Secretary Ashton Carter told CNN at a press conference Thursday that “it’s a matter of seeing what the Russians do.”

Carter said he hopes the Russians will fight ISIS, “but if it’s a matter of pouring gasoline on the civil war in Syria, that is certainly not productive from our point of view.”

Obama, Putin to meet at U.N. next week