South Korea has released a paper describing North Korea as its enemy for the first time in several years.

South Korea called the nuclear-armed North its "enemy" in a defence document on Thursday, the first time in six years it has used the term, signalling a further hardening of Seoul's position toward Pyongyang.

In the biennial report released on Thursday, North Korea's regime and military were described as "our enemy," which has not given up its nuclear ambitions and aims to unite the entire peninsula under its communist rule. 

During a period of detente in the 2000s, South Korea ceased using such enemy terminologies, but brought them back after 50 South Korean navy sailors were killed in a 2010 torpedo attack that Seoul blamed on North Korea.

The report said that North Korea has continued reprocessing spent fuel from its reactor and now has some 70 kilograms (154 pounds) of weapons-grade plutonium. That figure is up from 50 kilograms in a previous report for 2022, it said.

The document said Pyongyang's nuclear programs and tests were "seriously threatening our security."

"As North Korea continues to pose military threats without giving up nuclear weapons, its regime and military, which are the main agents of the execution, are our enemies," the document said.

The paper said the North had violated a 2018 inter-Korean military pact that bans hostilities on 15 occasions in the last year alone.

These included the firing of artillery inside a military buffer zone and the launching of missiles launched across the de-facto maritime border into the South in November.