People are getting worked up over these photos of US soldiers fighting ISIS in Syria

Photos of US soldiers wearing Kurdish People's Protection Unit (YPG) patches as they fight the Islamic State alongside Kurds in Syria have re-ignited the debate over Washington's support for the group, with some calling the patches "politically tone deaf" and others insisting it is "perfectly normal."

The YPG has proven to be the most effective force fighting ISIS on the ground in northern Syria, but the territorial expansion their victories have afforded them is vehemently opposed by Turkey, an important US ally and member of NATO.

Ankara views Kurdish demands for autonomy as a threat to Turkey's sovereignty and backs many of the rebel groups that have clashed with the YPG, which Turkey says is linked to the Kurdistan Workers' Party (PKK) - a designated terrorist organization currently waging an insurgency in Turkey's southeast.

As such, some analysts wonder whether the Americans' show of solidarity with the Kurds will further inflame tensions between the US and Turkey.

As one Kurdish activist asked on Twitter, "How will Erdogan react?"

Charles Lister, a Syria expert and senior fellow at the Middle East Institute, said it is "absolutely remarkable seeing US special forces personnel wearing YPG patches in the northern Raqqa operation."

"The US National Counterterrorism Center (NCTC) labeled the YPG the Syria wing of the 'designated' PKK in 2014," he added.

Emile Hokayem, a Middle East analyst at the International Institute for Strategic Studies, tweeted that the photos are "politically tone-deaf and counterproductive in this context." He was likely referring not only to the US-Turkey relationship, but also to the tension between Kurdish forces and Syrian Arab rebel groups associated with the Free Syrian Army.

Mutual distrust continues to cast a shadow over the Kurdish-Arab relationship in northern Syria, even as the Obama administration has tried to bring Arab and Kurdish forces together via the Syrian Democratic Forces (SDF) to fight the Islamic State.

FSA rebels were reportedly enraged, for example, when they learned that the US' top military commander, General Joseph Votel, visited Kurdish commanders in northern Syria last weekend to discuss the Kurdish-dominated SDF's plans to retake territory from ISIS.

Many FSA groups don't trust the Kurds - who wish to carve out an autonomous region in northern Syria known as Rojava - and are wary of the US' support for them.

"The Arab fighters [in the SDF] are just camouflage," General Salim Idris, the former FSA chief of staff, told Voice of America on Monday. "The SDF is the YPG, which collaborates with anyone - Assad, the Russians, the Americans - when it suits its purposes."

He added: "I really don't think the Obama administration has thought this through. Will the Kurds give up Arab towns they capture?"

Some analysts worry that photos of US soldiers showing solidarity with the Kurds by wearing YPG patches will infuriate FSA rebels - and Turkey - even further. 

But Wladimir van Wilgenburg, a field researcher for the Iraqi Institute for Strategic Studies and a journalist based in the region, said the practice is "quite normal."

"They do it out of respect for the local forces they are working with," van Wilgenburg told Business Insider on Thursday. "Its the same with coalition soldiers in Iraqi Kurdistan. I have seen them with Kurdish flags, or patches of different Peshmerga forces (like the Zerevani)."

He added: "It has nothing to do with politics. They are fighting together as a 'band of brothers' against the Islamic state, so it's quite normal."