The Assad regime sees all armed opposition as terrorist groups and Mr Assad said all foreign troops on Syrian soil without invitation or consultation with the Syrian government are considered "invaders".
US Military commanders have said they would like greater freedom to make decisions on the ground on how best to fight ISIS.
But the SDF now believes they have the strength in numbers to take Daesh's self-declared capital.
The newly deployed USA troops have been sent to the region to help "whoever is going to take Raqqa", a group that has yet to be determined, the official said. Turkey said it had "neutralized" 71 YPG fighters this week and occupies more than 2,000 square km in northern Syria.
This increase is shifting the United States from working quietly behind the scenes in Syria's conflict.
The area around Manbij has been controlled since a year ago by the Manbij Military Council, a local militia that is a part of the Syrian Democratic Forces (SDF), an umbrella organisation of armed groups of which the YPG is also a part.
The U.S. command said 13 strikes engaged targets including eight IS tactical units, four vehicles, a fighting position and an IS headquarters near Raqqa.
Moreover, while the USA and their coalition claims to be working to defeat IS in Raqqa, various reports state that the us - led coalition is carrying out airstrikes that target Syrian civilians, military, and infrastructure.More news: Six Nations 2017: Ireland ready for Cardiff noise - Best
When the U.S-backed, Kurdish-led Syrian Democratic Forces captured the town from IS in August, Turkey sent its troops into Syria, complaining to the Americans that the Kurdish forces must retreat east across the Euphrates. The operations are part of Turkey's months-long incursion into its war-torn neighbor in a push against IS but also in an effort to restrict the US -backed SDF.
Syria requested that the U.N. Security Council pressure Turkey to pull out its "invasion forces" from Manbij on Friday, a day after Ankara said it would attack any Syrian Kurdish YPG forces in their way.
"In Iraq, with eastern Mosul liberated and the fight to retake western Mosul ongoing, liberating the city from ISIS' control is an important step in defeating the enemy".
Such groups have apparently been favored by the USA, largely because they are consistent, organized, and more importantly have no jihadi background or religious motive behind their cause, Ahmad Ashqar, a Syrian journalist, told Xinhua.
Sheikh Ehmed said troops from the US -led coalition have increased in northern Syria and are playing a bigger role in the battle for Raqqa. In fact, the Financial Times notes that USA forces hung American flags on the gates of Manbij to send a signal that might prevent "a possible skirmish between the varied forces arrayed around the town".
Turkey and Russian Federation brokered a cease-fire in December and co-sponsored two rounds of talks this year between Syrian President Bashar Assad's government and the opposition.
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.
"It can not be from the air, it should be in cooperation with the troops on the ground, that's why the Russians succeeded, since they supported the Syrian Army in pushing IS to shrink, not to expand as it used to be before that".