Kim Song's comments at the world body headquarters in New York came just moments after South Korea's military said the North had fired an "unidentified projectile" into the sea off its east coast.

"Nobody can deny the right to self-defense for the DPRK to develop, test, manufacture and possess the weapon systems equivalent to the ones which are possessed or being developed by them," Kim said, referring to South Korea and the United States.

"We are just building up our national defense in order to defend ourselves and reliably safeguard the security and peace of the country," he added.

Pyongyang is under multiple sets of international sanctions over its banned nuclear weapon and ballistic missile programs.

It has already carried out several missile tests this month, one involving a long-range cruise missile and another with short-range ballistic missiles, according to the South's military.

Seoul recently successfully test-fired a submarine-launched ballistic missile (SLBM) for the first time, making it one of a handful of nations with the advanced technology.

Kim added that annual joint military exercises between the United States and South Korea and "the deployment of all kinds of strategic weapons" towards the North should be stopped "permanently."

The launch early Tuesday in the Korean Peninsula came as the North was due to open a session of its rubber-stamp parliament, the Supreme People's Assembly.