North Korea is highly likely to pursue military provocations toward the South amid growing internal instability, the ruling party chief said Thursday, calling for the military's watertight defense posture.

The warning by Saenuri Party Chairman Kim Moo-sung came after North Korea fired dozens of artillery rounds in a firing drill near the tensely patrolled maritime border in the Yellow Sea on Wednesday.

Last week, the North also claimed it test-fired a submarine-launched ballistic missile in violation of U.N. Security Council resolutions, escalating security jitters on the Korean Peninsula.

"Since the North Korean regime is unpredictable from a common-sense standpoint, provocations of any kinds are likely at any time," Kim said during a meeting of senior party members.

Many experts point to a growing stability in the North Korean regime's internal power structure and increasing opposition to the Kim Jong-un regime, the ruling party chief said. "These conditions significantly raised the possibility of North Korea launching provocations in order to quell internal discontent."

The South Korean military should be poised with watertight defenses to deal with such likely provocations, Kim noted.

The National Intelligence Service here said Wednesday the North has recently executed defense chief Hyon Yong-chul after he was seen dozing off during a military event attended by the young leader and dismissive of his instructions.

Intelligence officials said Kim Jong-un is increasingly dependent on a reign of terror in order to tighten his power grip. (Yonhap)