The Pentagon proposed deploying tanks to eastern Syria as an option to guard the region’s oil fields after the US was concerned Russia would cross a deconfliction line on the Euphrates River this week, a US official with knowledge of the situation told Al-Monitor.

Earlier this week, the US raised concerns that Russian forces might make a move to cross the river, which has served as a de facto marker between US-led operations to defeat the Islamic State and Moscow’s military campaign in support of Syrian President Bashar al-Assad, though Russian forces were not seen massing in the area.

At least two Trump administration sources confirmed there were concerns about putative Russian moves on Deir ez-Zor province, home to some of the war-torn country’s largest oil fields.

First reported by Newsweek, the option to deploy tanks near the oil fields gained momentum Wednesday night before marathon talks between American and Russian officials “at almost every level” neutralized the concern earlier on Thursday, said the official, speaking on the strict condition of anonymity.