LOS ANGELES (KTLA) — A Southern California man accused of attacking a flight attendant mid-air last week, causing the plane to be diverted to Denver, has been charged with assault, officials announced Monday.

The incident occurred Wednesday aboard American Airlines Flight 976 heading to John Wayne Airport in Santa Ana from New York City.

Authorities did not release details of the incident, but 20-year-old Brian Hsu, of Irvine, faces charges of interference with a flight crew and assault within the special aircraft jurisdiction of the United States, according to the Department of Justice.

The female flight attendant was apparently punched in the face repeatedly and suffered a broken nose.

Witnesses on the plane said the incident began when the passenger became upset over having to wear a facial covering during the flight, but American Airlines later said they had “no information suggesting the incident was mask compliance related.”

Passengers said Hsu had to be duct-taped to his seat after the attack. After the flight landed in Colorado, Hsu was “removed and apprehended,” the airline said.

He was expected to appear in District Court for the Central District of California on Monday.

The incident was investigated by the FBI with help from the Denver Police Department.

In a statement released after the incident, American Airlines said the passenger “will never be allowed to travel with American Airlines in the future, but we will not be satisfied until he has been prosecuted to the full extent of the law.”

“We are outraged by the reports of what took place on board,” the airline’s statement read. “Acts of violence against our team members will not be tolerated by American Airlines. We have engaged local law enforcement and the FBI and we are working with them to ensure they have all the information they need.”

Reports of unruly behavior on planes, including violence against crew members, have increased since the start of the coronavirus pandemic. The Federal Aviation Administration said 923 investigations have been initiated this year into violations of regulations or federal laws. The number is up from 183 last year and 146 in 2019.

Additionally, the FAA has been handing out hefty fines this year after a surge in these unruly passenger incidents, most of which are over mask mandates.