The U.S. military has begun bolstering its troop numbers in a swath of eastern Syria where President Trump has said he wants to protect oil fields, U.S. defense officials said Saturday.

The U.S. troops began arriving in Deir al-Zour province in a convoy from northern Iraq. The defense officials, speaking on condition of anonymity because of the sensitivity of the issue, said the forces will reinforce American troops in coordination with the Kurdish-led Syrian Democratic Forces, who have teamed with the Pentagon on operations against the Islamic State for years.

The additional forces will help “prevent the oil fields from falling back into the hands of ISIS or other destabilizing actors,” one U.S. defense official said.