A U.S. Border Patrol agent shot at three suspects early Monday after being assaulted on a residential street near the U.S.-Canada border, the agency said.

An officer on routine patrol spotted the three people — two male and one female — walking in Derby Line at about 2:15 a.m., said spokesman Mark Henry. The agent, who was not identified, spoke with the three people briefly before they began assaulting him, he said.

"They knocked him down, there was a struggle," Henry said. "One subject started punching and hitting him; at that point he became concerned for his life."

The agent fired two shots. A male and female suspect were taken into custody. The third person fled into Canada.

Neither person in custody was wounded. Agents don't know about the other suspect.

Henry said he couldn't release the names of those in custody and he didn't know their nationalities.

Derby Line is a series of residential streets and buildings that straddle the border.

In October, the Royal Canadian Mounted Police arrested more than 40 people trying to enter Canada illegally through Derby Line.

In August, a Border Patrol agent in Alburgh, Vt., fired his weapon at a car that had illegally entered the country after the driver tried to run him over. There have been no arrests in that case.