Relations between Turkey and the US deteriorated over American backing of the YPG, which has expanded its sphere of influence in northern Syria as it conquered vast tracks of land from Isis with the backing of American air power. This week's deployment is just the latest commitment to that aim. It also risks drawing troops into a long and costly war with unpredictable outcomes.
For his part, Colonel Talal Silo, the spokesman of the SDF, told Xinhua in a recent interview that the SDF fighters have become in control of 30 percent of the territory in northern Syria with the help of Washington.
The Pentagon this week announced that it had also sent extra troops into Manbij to prevent competing factions fighting each other in the former IS stronghold. "In that case, I think in what we are doing in Syria, we are looking at that as an extension of the - of the authority to operate from - from Iraq".
The troops expect to encounter far more fleeing civilians once they enter deeper into the more densely populated part of the city.
The plan's consisted of a strategy that would probably increase the number of United States troops in to better advise and assist the US-backed Syrian fighters who will go through the battle for Raqqa.
The fact that President Donald Trump's administration is still assessing what its Syria policy will be and is still reviewing its plan on how to fight ISIS adds to this uncertainty surrounding the Raqqa offensive.
However, the fight between Turkish backed forces and the YPG militia is a worrying sign as both are allies of the U.S. and clashes between them could impede America's efforts to establish a coalition to capture the Syrian city of Raqqa from Isis militants.
"Much like in Iraq, you will see coalition forces enabling logistics, intelligence, targeting and defending friendly forces arrayed against ISIS in Syria".
So does this mark the beginning of a more aggressive United States policy in Syria?
He added that the USA forces "are our partners within the anti-terror coalition and they have been with us in all of our operations".
With the advance of the SDF, the IS has lost all routes out of Raqqa, save for one through the Euphrates River, according to the Syrian Observatory for Human Rights monitor group.
But it is still seen as ill-equipped for the hard assault on militants entrenched in the city.
As the Marines were arriving, the US 75 US Ranger regiment carried out a very visible maneuver, driving around the outskirts of a town called Manbij flying the Stars and Stripes in a show of force to warn off Turkey and its Syrian rebel allies.
Partnering with the Kurds to take Raqqa could also cause major damage to the USA relationship with North Atlantic Treaty Organisation ally Turkey.
"If the USA were to prefer terrorist organizations over Turkey in the fight against IS, that would be their own decision, but that wouldn't be something we would consent" to, Yildirim told The Associated Press. However, Turkish president Recep Tayyip Erdogan said in Moscow on Friday after talks with Vladimir Putin that Turkey was co-operating entirely with Russia's military over Syria, and also wants to work with the US-led coalition in targeting Manbij.
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