SEOUL, Feb 16 (Reuters) - South Korea released its latest defence white paper on Thursday, describing North Korea as its "enemy" for the first time in six years and reporting an increase in Pyongyang's stockpile of weapons-grade plutonium.

The biennial white paper offers a glimpse into the reclusive North's growing arsenal of nuclear weapons and missiles, as well as its conventional military capabilities.

The 2022 paper revived the description of the North Korean regime and military as "our enemy," last used in its 2016 edition, citing Pyongyang's ongoing weapons development, cyber and military provocations and its recent portrayal of the South as an "enemy."

"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.

To beef up its nuclear stockpile, North Korea has continued reprocessing spent fuel from its reactor and possesses about 70kg (154lb) of weapons-grade plutonium, up from 50kg estimated in the previous report, it said.

The North has also secured "substantial" amounts of highly enriched uranium" and "significant level of capability" to miniaturise atomic bombs though six nuclear tests, a description that remains unchanged since 2018.

"Our military is strengthening surveillance as the possibility of an additional nuclear test is rising," the paper said, citing the restoration last year of previously destroyed tunnels at the North's testing site.

The paper said the North violated a 2018 inter-Korean military pact banning hostilities 15 times last year alone, including its drone intrusion in December, artillery fire inside a military buffer zone and missiles launched across the de facto maritime border into the South in November.

Its 2020 edition said the North was "generally" complying with the agreement, which was sealed on the margins of a 2018 summit between North Korean leader Kim Jong Un and then-South Korean President Moon Jae-in.

The latest document noted Pyongyang's 2022 launches of intercontinental ballistic missiles, including the new Hwasong-17 tested, but said further analysis was needed to verify whether it has acquired improved missile re-entry technology.

On Japan, the paper called it a "close neighbour that shares values" for the first time since 2016, amid efforts to mend ties strained by history and trade spats.