A U.S. border patrol agent was assaulted while attempting to apprehend a group of illegal immigrants crossing the border in California on Tuesday.

The unidentified agent was patrolling near the Calexico West Port of Entry and the New River when he came across a group of individuals trying to cross the border from Mexico.

The agent, who was by himself, was able to detain one man and place him in custody in the back of his service vehicle. When he turned his attention to the rest of the group, another member of the group exited the river and opened the rear passenger door, allowing the man in custody to attempt an escape.

The two men ran towards the river and the agent pursed them.

“He was resisting arrest, actively resisting, pulling away. While the agent was trying to make the arrest other members of the group began to throw rocks and other objects, verbally shout threats at the agent,” Agent Justin Zaffuto told KYMA.

The agent suffered minor injuries, officials said.

The border-crosser who had originally been placed inside the vehicle was re-apprehended. He faces federal criminal charges for the alleged assault on the agent.

The rest of the group fled back to Mexico.

“The New River and immediate surrounding area remains one of our most challenging and dangerous areas to work,” El Centro Sector Assistant Chief Patrol Agent David Kim said in a statement. “The border wall system replacing the old fencing in that area is a solid step in mitigating those challenges.”

Zaffuto told KYMA that physical attacks on agents have increased this year.

“Compared to last year, we had 23 all year,” he said. “This year so far, we’ve had 80 assaults on agents. A lot of the times, agents are working by themselves.”

He continued: “It’s a 24-hour operation. You might be in areas where it’s dark, completely dark and you encounter a large group. Just the numbers alone is a disadvantage.”