Local police confirmed to Fox 13 they were helping execute two federal search warrants.
In cell phone video of the incident, five shots of apparent flash bangs were aimed at the trailer in just over a minute.
Neighbors witnessed FBI agents and police K-9s trying to get a man out of a home near 400 North and 200 West.
"I [had] seen the flash come out of the trailer and people yelling," said the neighbor who took the video and asked to remain anonymous. "That’s when I knew something was up."
Within minutes of seeing a flash inside the trailer, law enforcement officers were heard yelling, "There’s a fire. A fire!"
Smoke quickly turned into flames; the man inside the trailer appeared to stay inside as local law enforcement moved back.
“I was wondering if he was going to be okay," the neighbor said. "They were still yelling for him to come out. The trailer was on fire for a while before he exited the trailer.”
An FBI spokesperson in Salt Lake City would not confirm what happened, if anyone was hurt, or why FBI agents were at the site.
“I can confirm that the FBI was conducting court-authorized activity in Vernal today but because it is related to an ongoing case, I can’t provide any more details,” said FBI Spokesperson Sandra Barker.
A second incident involving the FBI happened in nearby Naples, Utah, on Thursday, according to the police chief.
He confirmed to Fox 13 his agency helped execute a federal search warrant for the FBI with the help of the Uintah County Drug Task Force and other local police agencies.