DAMASCUS, Oct. 7 (Xinhua) -- The Turkish military campaign against the Kurdish-led Syrian Democratic Forces (SDF) began on Monday night in northern and northeastern Syria, Syria's state TV and activists reported.

The state TV in Syria said the Turkish attack targeted the SDF-held Tal Tawil area in the northeastern countryside of Hasakah province in northeastern Syria, branding the attack as a "Turkish aggression."

The Turkish attack also targeted the SDF positions in the Tal Abyad city in the northern countryside of Raqqa province in northern Syria amid the flight of Turkish warplanes in the region, said the TV.

The state TV aired some footages purporting to show night shelling by Turkish forces on the aforementioned area, saying there is no human losses from the Turkish attack in Tal Tawil.

On the opposition side, activists said the Turkish warplanes struck SDF positions near the Semalka Border Crossing, which is established between the Kurdistan Regional Government in Iraq and the Kurdish-held areas in north and east of Syria and located in the eastern countryside of Hasakah.

The Syrian Observatory for Human Rights war monitor said that 80 truckloads of logistics and weapons crossed the Semalka Border Crossing into SDF-held areas on Monday.

The Turkish attack comes as Turkey has been threatening recently to start a military operation in northeastern Syria against the Kurdish-led groups, which it deems as terrorist groups.

It's not yet clear whether the attack is a fully-fledged one or just a limited one.

It's worth noting that the Syrian state media outlets have been branding the SDF as a "separatist Kurdish movement" as this group and its broader umbrella of the People's Protection Units (YPG) control areas in northern and northeastern Syria with the backing of the United States.

Earlier in the day, the United States pulled out forces from observation points in northeastern Syria along the borderline with Turkey amid threats by Ankara to launch a military campaign against the Kurdish forces, according to the Observatory.

The U.S. withdrew forces from observation posts at Tel Abyad and Ras al-Ain in northeast Syria.

On Saturday, Turkish President Recep Tayyip Erdogan unleashed his strongest warning yet, threatening to launch a military operation against the U.S.-backed Kurdish militia groups in northeastern Syria.

In August, the U.S. and Turkey agreed to have joint patrols into designated Kurdish areas near the Turkish border as a prelude to imposing a safe zone.

In his speech on Saturday, Erdogan said the deal with the U.S. to secure the border with Turkey was faltering.

Meanwhile, the SDF said in a statement Monday that the U.S. didn't live up to its pledges to defuse the tension with Turkey despite the "flexibility" the Kurdish militia has shown regarding the U.S.-Turkish understanding to create a safe zone in northern Syria.

The SDF said that the Turkish campaign will undermine the SDF war on terrorist groups such as the Islamic State (IS) and will endanger the security and safety established in Kurdish-controlled areas in northeastern Syria.

On the ground, the Turkey-backed Syrian rebels started crossing from Syria into the Turkish territories on Monday to be transported to areas opposite to the Kurdish-controlled parts in northeastern Syria as part of the preparations for the Turkish campaign.

Turkey sees YPG and its allied SDF as separatists and terrorists, citing their links with the Kurdistan Workers' Party (PKK), which is listed as a terrorist organization by Turkey, the United States, and the European Union.

The Kurdish militia forces have been controlling areas in northern Syria since the early years of the crisis in Syria, in order to force Damascus to recognize a federal rule or autonomy for the Kurds in northern Syria.

However, Syrian government officials repeatedly said that Kurdish federalization in Syria or self-rule is out of the question.

In 2018, the Kurdish forces lost the Afrin enclave in the northern countryside of Aleppo province in northern Syria to the Turkey-backed rebels.

At the time, the Kurdish fighters were advised to establish an agreement with the Syrian government to let the Syrian army deploy in Afrin and to allow the government institution back to that area to strip Turkey of its pretext to launch a military operation against Afrin.

However, the SDF and YPG back then didn't accept the control of the Syrian government over Afrin and as a result, they lost it to Turkey.

In its coverage on Monday, the national Syrian TV hosted political experts who said that the Kurdish militia must return to Damascus in order to avert other Kurdish-controlled areas the fate of Afrin.

Meanwhile, the Iranian al-Alam TV said that Iran's Foreign Minister Mohammad Javad Zarif called his Turkish counterpart Mevlut Cavusoglu on Monday night, during which Zarif called for respecting Syria's sovereignty.

According to the report, Cavusoglu informed Zarif that Turkey will not undermine the Syrian sovereignty and that the Turkish military campaign will be temporary.