AJO, ARIZ. -- The U.S. Border Patrol agent's union reported that Mexican soldiers crossed into U.S. territory and held an agent captive at gunpoint during a Sunday night incident.

The National Boder Patrol Council Local 2544 in Tuscon reported on its website that reported that the incident occured near Ajo, Arizona.

The union website reported that the soldiers returned to Mexico without further incident after reinforcements arrived to confront them.

It's not clear why Mexican soldiers were on U.S. territory but union officials said in their website that Mexican soldiers have been known to protect Mexican drug gangs and migrant smugglers.

"Unfortunately, this sort of behavior by Mexican military personnel has been going on for years," Union Local 2544 of the National Border Patrol Council said on its Web page. "They are never held accountable, and the United States government will undoubtedly brush this off as another case of, 'Oh well, they didn't know they were in the United States.' "

The union website said Tuscon Sector agents were grateful that the incident ended without gunfire but reserving further comment on the issue until agency leaders handle the situation.

United Press International reported that both State Department and Border Patrol officials in Washington DC declined to comment on the incident on Wednesday.

Read more about the incident and others like it at Local 2544's website:

http://www.local2544.org/home.asp