Nguyen Viet Manh, 36, from the northern province of Thai Binh, is being investigated for illegal possession of military weapons.
Manh was arrested Tuesday night as he arrived at a port in Ho Chi Minh City on Phuong Nam 1, which was sailing from the Philippines.
Hai’s actions made border guard officers suspicious and they decided to stop him and search his suitcase.
Manh told the officers he was going to sell the guns, made in the U.S., and the ammo in the city.
In line with the current laws in Vietnam, illegal possession or trade in military weapons can be punished with jail terms of one to seven years.