The United States is currently building two new military bases in the north of Syria, more specifically in the Manbij region. This means the American army shifts slightly closer to the Euphrates and towards the area controlled by the Turkish army.
According to the Turkish news agency Anadolu, building materials and machines are currently being supplied to the area. There were also about 300 American soldiers and various armored vehicles in Manbij, bringing the total US occupation in the area to around 2,000 soldiers.
It seems that with this move the US military wants to stop a further advance of the Turkish army in the area. Earlier, Turkish President Erdogan expressed his dissatisfaction with the American plan to build a Kurdish army of 30,000 men, after which he decided to invade the Kurdish part of Syria.