Free Syrian Army rebels supported by Turkey have attacked the predominantly Kurdish Syrian Democratic Forces (SDF) alliance, which has the US' backing as its most effective ally on the ground.
The Pentagon said Monday that USA forces have also taken up positions on the outskirts of Manbij to try to keep a lid on tensions.
"An attempt to capture Manbij would mean confrontation with three critical actors in Syria, namely the U.S., Russian Federation and Syria as well as Iran", Ilhan Uzgel, a senior analyst in global relations, told Xinhua.
President Donald Trump promised on the campaign trail to "knock the hell out of" Daesh, saying he would put US forces on the ground to take the fight to the terror group.
The Syrian government, which Turkey does not recognize as legitimate, considers the presence of Turkish troops on its territory as aggression.
The group said it delivered food and other supplies including clothes and blankets to between 350,000 and 500,000 Syrians across the border in Syria each month.
The meeting of the top brass came ahead of a visit by Turkish President Recep Tayyip Erdogan to Russian Federation.
The top brass of Turkey, Russia and the United States military met Tuesday to increase their coordination in Syria in their fight against Islamic State.
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"Turkey told its counterparts that no terror group can be destroyed by using another terror group", he said in Ankara.
Last week Russian fighters launched airstrikes against a US camp in Syria, which had been training anti-Assad Syrian militiamen battling Islamic State. The U.S. would continue to designate the PKK as terrorists, despite knowing the organic links in between, but would not call the YPG as terrorists.
Euphrates Shield is the name of the operation Turkey launched inside Syria last August targeting the Islamic State group and the SDF, which is dominated by Kurdish fighters that Ankara sees as "terrorists".
Turkish Prime Minister Binali Yildirim said the meetings would continue on Wednesday.
Turkey has sought the support of the USA, its North Atlantic Treaty Organisation ally, to lead a ground offensive against Islamic State's main Syrian stronghold of Raqqa that would advance through areas controlled by Kurdish fighters, a Turkish official said last week.
Photographs and videos posted on social media in recent days have shown convoys of USA troops, including Stryker armored vehicles and Humvees, heading through the northern Syrian countryside trailing big Stars and Stripes flags.
The volatile situation in and around Manbij is worrisome for the USA on several levels, including a concern that additional conflict there could detract from US efforts to mold a Syrian opposition force capable of recapturing Raqqa, the IS self-declared capital. Despite Turkey's strong opposition, it favors the participation of the YPG's political wing in the Geneva peace talks. American forces have carried out training and advising missions in the city.
"Disintegration of states in the Middle East would have disastrous consequences", he warned.