The main reason for the increase in US pressure on Turkey to stop its attacks in northern Syria is that one of the airstrikes conducted by Turkey last week hit a target that was less than a quarter of a mile from US troops in the area, Axios reported, citing a US source.

Turkey has increased artillery and airstrikes on northern Syria in recent weeks and has said it is preparing for a possible ground operation against Syrian Kurdish fighters that it says are terrorists but who make up the bulk of the US-backed Syrian Democratic Forces (SDF), who helped a coalition of Western powers fight against the Islamic State in Iraq and the Levant (ISIL).

“We don’t want to see military operations conducted in northwest Syria that are going to put civilians at greater risk than they already are, put in peril our troops and our personnel in Syria, or our counter ISIS mission,” Kirby told reporters on Wednesday.

The same day, Axios reported that Central Intelligence Agency (CIA) Director Bill Burns warned Turkey’s National Intelligence Organization (MIT) chief Hakan Fidan about recent Turkish artillery strikes and airstrikes against Kurdish targets in northern Syria, saying that they put US forces in danger.

Citing US sources, Axios said several of the airstrikes that US officials said endangered American forces in northern Syria were conducted by the Turkish intelligence service using drones.

The Turkish strikes were launched after a blast in central Istanbul killed six people and wounded 81 on Nov. 13. Turkish President Recep Tayyip Erdogan said Turkey was more determined than ever to secure its border with Syria from attacks by Kurdish forces, threatening a ground operation “at the most convenient time.”

Presidential spokesman Ibrahim Kalın also said in late November that Turkey’s ground offensive in northern Syria could take place “tomorrow, next week or at any time.”

Although Ankara claims Kurdish forces in Syria were behind the Istanbul bombing, no group has claimed responsibility, and the SDF and the outlawed Kurdistan Workers’ Party (PKK) denied involvement.

The US has 900 soldiers in northern Syria, most of them stationed at bases that belong to the SDF.

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