Washington (CNN) The US-led coalition fighting ISIS has observed pro-Syrian regime forces once again conducting a slow build-up east of the Euphrates River near where US troops are present advising local allies, according to multiple US and coalition officials.

The pro-regime forces are assembling near where similar forces allied with Syrian President Bashar al-Assad initiated an unprovoked attack on US-backed Syrian Democratic Forces, US Army Col. Ryan Dillon, a spokesman for the coalition told CNN.

Dillon added that the coalition was keeping a close eye on the activity and was communicating with their Russian counterparts via the de-confliction hotline to discuss the development.

He said the coalition hoped to "first deescalate the situation" but added "if it comes down to it we will defend ourselves."

The coalition was also on the lookout to see if pro regime forces bring in any combat equipment, like artillery, that could threaten coalition troops.

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