The US President Donald Trump has approved an expanded military occupation to secure an expanse of oil fields across eastern Syria, raising a number of difficult legal questions about whether US troops can launch strikes against Syrian, Russian or other forces if they threaten the oil, US officials said.
The decision, coming after a meeting on Friday between Trump and his defence leaders, locks hundreds of US troops into a more complicated occupation in Syria, despite the president's vow to get America out of the war.
Under the new plan, troops would protect a large swath of land controlled by the YPG, the Syrian wing of the PKK that stretches 150 km from Deir el-Zour to al Hassakeh, but its exact size is still being determined.
The PKK is recognised as a terrorist group by the EU, US, and Turkey and is responsible for more than 40,000 deaths in Turkey over the last several decades.
US officials said many details still have to be worked out. But, Trump's decision hands commanders a victory in their push to remain in the country to prevent any resurgence of Daesh, counter Iran and a means to continue the controversial partnership the YPG.
But it also forces lawyers in the Pentagon to craft orders for the troops that could see them firing on Syrian regime or Russian fighters trying to take back oil facilities that sit within the sovereign nation of Syria.
The officials spoke on condition of anonymity in order to discuss internal deliberations.
Trump's order also slams the door on any suggestion that the bulk of the more than 1,200 US troops that have been in Syria will be coming home any time soon, as he has repeatedly promised.
The Pentagon will not say how many forces will remain in Syria for the new mission. Other officials, also speaking on condition of anonymity to discuss ongoing deliberation, suggest the total number could be at least 800 troops, including the roughly 200 who are at the al Tanf garrison in southern Syria.
According to officials, lawyers are trying to hammer out details of the military order, which would make clear how far troops will be able to go to keep the oil in the YPG/PKK's control.
The legal authority for US troops going into Syria to fight Daesh was based on the 2001 and 2002 Authorizations for Use of Military Force that said US troops can use all necessary force against those involved in the September 11 attacks on America and to prevent any future acts of international terrorism.
So, legal experts say the US may have grounds to use the AUMF to prevent the oil from falling into Daesh's hands.
But protecting the oil from Syrian regime forces or other entities may be harder to defend.
"The US is not at war with either Syria or Turkey, making the use of the AUMF a stretch," said Stephen Vladeck, a national security law professor at the University of Texas at Austin.
He added that while the US Constitution bestows significant war powers on the president, those are generally meant to be about self-defence and for the collective defence of the country.
Arguing that securing the oil is necessary for national security "just strikes me as a bridge too far," he said.
Members of Congress, including Democratic Senator Tim Kaine, have also raised objections to the Trump administration using the AUMF as a basis for war against a sovereign government. That type of action, he and others have argued, required approval by Congress.
US officials said the order approved by Trump does not include any mandate for the US to take Syria's oil. Trump has said multiple times that the US is "keeping the oil." But the White House and the Pentagon have so far been unable to explain what he means by that.
Defense Secretary Mark Esper said Friday he "interprets" Trump's remarks to mean the military should deny Daesh access to the oil fields.
There were already a couple of hundred US troops around Deir el Zour, and additional forces with armoured vehicles, including Bradley infantry carriers, have begun moving in. Officials have said the total force there could grow to about 500.
Trump, Esper and other defence leaders have said it's important to protect the oil so that Daesh can't regain control of the area and use the revenues to finance their operations.
Currently, the US-backed Syrian YPG/PKK terrorists have controlled the oil, supported by a small contingent of US troops. A quiet arrangement has existed between the YPG/PKK and the Syrian regime, whereby Damascus buys the surplus through middlemen in a smuggling operation that has continued despite political differences. The YPG/PKK sells crude oil to private refiners, who use primitive homemade refineries to process fuel and diesel and sell it back to the administration.
It's unclear how long that agreement may continue.
And if some dispute arises, US troops must have clear guidance on how to respond.
US forces can use military force to protect themselves. But the oil fields are expansive, and troops can't be everywhere.
If, for example, Syrian regime forces try to retake a portion of an oil facility and US troops are not nearby, it's unclear now how much force they could use if they aren't acting in self-defence.