Syrian government warplanes on August 20 flew over a flashpoint northeastern city despite a warning from U.S. officials against making air strikes where it has military advisers.

It was the third successive day that Syrian planes had either flown over or attacked positions in the city of of Al-Hasakah held by Kurdish forces fighting against Islamist fighters and forces loyal to the government of Syrian President Bashar al-Assad.

The U.S. military scrambled its fighter planes on August 19 and flew over Al-Hasakah within about 1.5 kilometers of two Syrian SU-24 fighter jets in an effort to "encourage" them to leave the area, a U.S. defense official told CNN.

Pentagon spokesman Captain Jeff Davis said on August 19 that U.S. forces have increased combat air patrols near Al-Hasakah and warned Damascus that Washington will defend coalition troops from attacks.

Davis said there are a small group of U.S. commandos in the area training and advising Syrian Democratic Forces fighting to oust President Assad.

Syrian warplanes had bombarded positions held by the U.S.-backed Kurdish forces on August 18.

Turkish Prime Minister Binali Yildirim said on August 20 that the bombing raids by the Syrians showed that Damascus was starting to see Kurdish attempts to gain territory in northern Syria as "a threat."

Yildirim said Turkey would play a "more active" role in the next months in Syria, without giving details.

Ankara sees the Syrian Kurdish militia in Syria as an offshoot of the outlawed Kurdistan Workers Party (PKK).

More than 250,000 people are estimated to have been killed in Syria since the civil war began in March 2011.

Based on reporting by AFP and CNN