The Turks had threatened to attack Manbij which is being held by U.S. allies, known as the Syrian Democratic Forces.
In addition to the Marines, about 100 soldiers with the 75th Army Ranger Regiment are deployed in and around Manbij, Syria, with Stryker armored fighting vehicles. Deir al-Zor province is nearly completely in the control of IS, also known as ISIS.
If the death toll is ultimately true, it may hinder the YPG's intention to attack ISIS itself, as YPG forces continue to build up around the ISIS capital of Raqqa, but probably can not sustain such an offensive while fighting Turkey at the same time.
The Trump administration believes that the pressure on ISIS in Raqqa is a crucial part of the general fight against the murderous terrorist organization.
It is unclear whether US -backed Syrian Democratic Forces - which include the Kurdish YPG, Turkish-backed Syrian opposition, or some combination of the two forces - will serve as the liberating force in Raqqa once the city is completely isolated.
"Our intention here with this - and this fell within the authorities that are provided to me right now - was to ensure that we had redundant capable fighters support on the ground to support our partners and ensure that we could take advantage of opportunities and ensure the continuing progress that we've been seeing", Votel said.
The Russian military says its warplanes have killed more than 600 militants in just one week while backing the Syrian army's offensive against the Islamic State group.
Turkey will not participate in the Raqqa operation, Yildirim said, if the US does not heed the warning that was repeated this week by several Turkish politicians here, .
Commanders on the ground were frustrated by what they considered micromanagement by the Obama administration, it adds.
The latest dispatch of around 200 Marines into northern Syria brings the number of United States boots on the ground in Syria close to more than 700.
The 4,500 service members assigned to the 11th Marine Expeditionary Unit left San Diego in October on a routine deployment.
The Turkish military which supports an alliance of Arab-Syrian and Turkish fighters said that 71 Kurdish fighters of the YPG and the PKK were killed over a period of a week.
Turkey has threatened to take over Minbij as part of a military campaign in northern Syria. SDF has captured wide areas from IS since then, under the cover of airstrikes by the USA -led coalition. "We'll have real weight in the Middle East", one Kurdish representative told the Financial Times.
President Vladimir Putin is hosting his Turkish counterpart, Recep Tayyip Erdogan, for Syria-focused talks.
And a US-backed coalition of Arab-Kurdish fighters are closing in on Raqa, manoeuvring to isolate the city from the rest of Syria's jihadist-controlled territory.
Cihan Sheikh Ehmed says the SDF has been on the offensive in the Raqqa area since November and have closed major supply roads used by the Islamic State group.
"To get to this second Islamic State from any European country, it's a couple of days on the bus". Leader Abu Bakr al Baghdadi has survived despite frequent reports of his death in airstrikes, and there are still thousands of militants fighting for ISIS.
Syrian forces and their allies Thursday entered Jarrah airbase, 16 kilometers south of Al-Khafsa, for the first time since 2014, the Observatory said.