The United States scrambled fighter jets to protect Syrian Kurdish forces, the Pentagon said Friday, as Syrian warplanes bombed the northeastern city of Hasakeh for a second day.

The US-backed Syrian Kurdish YPG militia has been clashing with regime forces in the city since Wednesday, adding a new dimension to the country's war as Syrian government troops and the YPG militia have seldom fought each other in a sustained manner.

The latest round of fighting is some of the most intense and represents the first time the regime has used its air force against the Kurds, with which about 300 American special operations advisors are embedded.

Pentagon spokesman Capt. Jeff Davis said US fighter jets were sent on Thursday to protect coalition forces, but Syrian warplanes had already left the area by the time they arrived.

"We did make clear that US aircraft would defend troops on the ground if threatened," he said. "We will ensure their safety, and the Syrian regime would be well-advised not to do things that place them at risk. We view instances that place the coalition at risk with utmost seriousness, and we do have the inherent right of self-defense."

Thousands of civilians fled north of Hasakeh

The coalition is now conducting more air patrols in the area, Davis said. That didn't appear to deter Syrian warplanes, which on Friday again carried out airstrikes.

The fighting has forced thousands of civilians to flee north and killed dozens, Kurdish media and officials said.

Most of Hasakeh city, the capital of the province with the same name, is under control of the YPG, but the regime has maintained control of other parts of the city during the five-year war.

The two sides have mostly avoided direct fighting but have periodically clashed in Hasakeh and Qamishli, a city near the border with Turkey, where the regime also controls some neighborhoods and the airport. The Kurds and the regime have often cooperated against rebel factions, particularly in Aleppo.

The Kurds control much of northeastern and northern Syria along the Turkish border, where they have set up an autonomous administration since the regime withdrew in 2012 to focus on rebel groups seeking President Bashar al-Assad's ouster.

The clashes appear to be in response to a recent Kurdish demand that pro-government National Defense Forces militia leave Hasakeh.

A government source in the city told the AFP news agency that the airstrikes were "a message to the Kurds that they should stop this sort of demand that constitutes an affront to national sovereignty."

Fighting in Hasakeh comes less than a week after the US-backed Syrian Democratic Forces (SDF), an umbrella of Arab and Kurdish militia, retook the strategic city of Manbij from the "Islamic State." That victory opened the possibility that they may advance further west in a bid to completely seal the Turkish border.

In a statement on Thursday, the YPG said the regime was trying to undermine SDF and YPG successes in Manbij.

The Syrian military said in a statement released on Friday that the fighting resulted from Kurdish forces trying to take over the city. The statement said the military's response was "appropriate" and that further attacks would be met with force.

cw/sms (AFP, AP, dpa, Reuters)