SAN DIEGO (Border Report) — Members of Mexico’s National Guard stopped a U.S. citizen on Wednesday as he attempted to cross the border into Mexicali with 600 rounds of ammunition, Mexico’s customs agency said.

Mexicali is about 120 miles east of Tijuana.

The man, who was only identified as a 58-year-old U.S. citizen, reportedly also had two small packets of marijuana, which is illegal in Mexico.

Officials said he was in a truck hauling a small trailer when he got the green light as he entered Mexican territory, meaning he didn’t have to stop for inspection. Nevertheless, members of the National Guard decided to pull him over.

They say he became nervous when asked what was in the trailer, which prompted the soldiers to search both vehicles.

They discovered the 600 .45-caliber bullets and the marijuana.

The ammo and the pot were turned over to police. The driver was also taken into custody.

Guns and ammunition are illegal in Mexico. Only the military, police agencies and those with special permits are allowed to carry guns south of the border.