It was speaking at a UN session on controlling weapons of mass destruction.
Archbishop Bernardito Auza, the Vatican's permanent observer, said conventional arms have the same effects as nuclear, chemical, and biological weapons.
He said: "The Holy See recommends that discussions on weapons of mass destruction go beyond the traditional categories of nuclear, chemical, biological, and radiological weapons to include devastatingly powerful conventional weapons used to perpetrate war crimes and crimes against humanity.
"Military forces, rebels, terrorists and extremist groups use with greater frequency ever more powerful conventional weapons, showing scant regard for civilian immunity, discrimination, or proportionality."
He went on to say that: "conventional weapons are becoming less and less "conventional" as technological advances elevate their power to destroy to the level of weapons of mass destruction."
The Vatican stressed its opposition to all weapons and urged the gathered international community to uphold existing treaties and to review definitions of what a weapon of mass destruction is.
Archbishop Bernardito Auza concluded by saying: "There is no doubt that every step towards banning weapons of mass destruction is a giant step towards achieving a better world."
The Vatican has previously called upon nations that manufacture and sell weapons to restrict sales countries deemed 'unstable.'
