(CNN) Syrian rebel fighters backed by Turkey went on a looting spree in Afrin on Sunday after seizing control of the Kurdish-held town following a two-month siege, observers said.

After forcing Kurdish fighters from their enclave in northwest Syria, the rebels pillaged private property, political and military sites, according to the UK-based Syrian Observatory for Human Rights (SOHR).

Some locals told SOHR that their houses were completely stripped of their contents.

A Turkish photographer on assignment for Agence France-Presse, who captured the chaotic scenes, told CNN that the looting was widespread and organized, adding that he saw hundreds of opposition fighters more focused on pillaging than celebrating their victory.

"They are looting everything; goods, animals, goats, even pigeons," Bulent Kilic said. "I've been in war zones for many years now. Two, three guys looting, it happens. I didn't even take much notice at first. But then I saw that they were in such a hurry to take everything from this city."

Ibrahim Kalin, a spokesman for Turkish President Recep Tayyip Erdogan, told CNN on Monday that Ankara was looking into the reports of looting, and suggested that some groups in Afrin might not be following orders from their commanders.

Rebels loot shops in Afrin.

Turkey, a NATO ally, launched an operation targeting Kurdish groups -- some backed by the United States -- in Afrin in January to clear the border area of militias it considers to be terrorist organizations.

More than 150,000 people have been displaced in the last few days from Afrin town, a senior Kurdish official and a monitoring group said over the weekend.

The UN said last week that it had received reports of opposition fighters looting the homes of some residents who fled Afrin.

A senior field commander for the Free Syrian Army, a rebel group involved in the battle for Afrin, blamed "some bad apples" within its forces but suggested the looting was not widespread.

A fighter tows looted items in a trailer.

"There were some mistakes committed by some members of the FSA yesterday in Afrin, we don't want these mistakes to happen again. The properties of the civilians should be left as they are," the commander told CNN on Monday. "There are some bad apples, but the good ones surpass the bad ones by far."

The commander's characterization of "some bad apples" seemed at odds with what Kilic photographed: a masked man driving a tractor laden with motorbikes, rebels in uniform carrying stacks of soft drinks and crates of food, and a fighter clutching a goat in the bed of a truck.

On Sunday night a traffic jam snarled the road leading into Afrin, with cars entering the town empty and returning to nearby Azaz, where Kilic was staying, packed with goods.

Kilic said some battalions spray-painted their names on certain shops as a way of "reserving" them for future looting.

Afrin's residents are enraged over the scale of the robbery, and many are trying to return to protect their homes and shops, Kilic said.

Rebel fighters walk past a burning shop in Afrin.

Erdogan: 'Our target is not invasion'

Speaking in Ankara on Monday, Erdogan said the previous day's events marked an important phase in Operation Olive Branch -- the invasion of Afrin -- and that forces would push eastward towards other Kurdish-held towns in northern Syria and across the border into Iraq.

"Our target is not invasion. Our target is to clear the terrorists," Erdogan said.

But the senior FSA commander said that in light of the looting, pro-Turkish forces might not be so quick to advance.

"If we don't improve the image we have in Afrin in the next 10 days or so, no one will dare say we want to go to Manbij," the commander said.

Three Kurdish militias -- the Kurdish Democratic Union Party (PYD), the People's Protection Units (YPG) and the Kurdistan Workers' Party (PKK) -- have borne the brunt of Turkey's offensive in Afrin.

The YPG is considered the backbone of the US-backed Syrian Democratic Forces, which was instrumental in eliminating ISIS' territorial foothold in Syria.

But Ankara says the YPG is an extension of the PKK, a group considered a terrorist organization by Turkey, the US and the European Union.

Syria, EU, US concerned about Afrin developments

Syria's Foreign Ministry on Monday called on Turkey to immediately withdraw from Afrin, saying in two letters sent to the UN Secretary General and the head of the UNSC that Turkey's occupation of the city was "illegal and contradicts the principles and purposes of UN Charter and international law," state-run news agency SANA reported.

"The Turkish practices and attacks not only threaten the lives of citizens and the unity of Syrian territory and people, but also prolong the war on Syria," the Ministry said, according to SANA.

EU Foreign Policy Chief Federica Mogherini told reporters in Brussels on Monday that she was worried about the situation in Afrin.

Mogherini said international efforts in Syria were aimed at "de-escalating the military activities, and not escalating them," and urged Turkey, Russia and Iran to work on de-escalation zones as promised.

On Monday, the US State Department called on all actors in the region to focus on fighting ISIS, which it says has been re-building as priorities have shifted elsewhere.

"The fighting in western Syria over the last two months, including in Afrin, has distracted from the Defeat ISIS campaign and provided opportunity for ISIS to begin reconstituting in some areas. This is a serious and growing concern. We call on all actors in Syria to remain focused on this significant threat from ISIS," State Department spokeswoman Heather Nauert said in a statement.