South Korea will further boost its military capabilities to counter North Korea's short-range missile threats, the defense ministry said Wednesday, after Pyongyang vowed to bolster its nuclear arsenal amid a deadlock in negotiations with the United States.

Wrapping up an eight-day congress of the ruling Workers' Party on Tuesday, the North's leader Kim Jong-un called for enhancing the country's "nuclear war deterrent" and building "the most powerful military strength."

Asked to comment on the South's preparations against such threats, defense ministry spokesperson Boo Seung-chan said an analysis is under way on the North's military build-up plan rolled out at the congress.

"Through the modernization of forces, our military has the capabilities to counter North Korea's short-range missiles, and will further boost them down the road," Boo told a regular press briefing.

During the congress held for the first time in nearly five years, the North's leader ordered work to make "nuclear weapons small, lighter and tactical and steadily push ahead with the production of super large nuclear warhead."

He also boasted of a new nuclear-powered submarine under development and called for improvement in its missile strike capabilities targeting objects in the range of 15,000 kilometers, apparently intended to be capable of reaching the mainland US.

The North Korean leader held three meetings with US President Donald Trump, but denuclearization talks have made little progress since their no-deal summit in Hanoi in February 2019.

The North was expected to hold a military parade after the congress but its state media has not yet mentioned whether it has held one.

On Wednesday, Kim's powerful sister, Kim Yo-jong, slammed the South Korean military for tracking signs of a parade, calling it an "idiot" that tops "the world's list in misbehavior"

Seoul's Joint Chiefs of Staff did not comment on the younger Kim's remarks and said they had no further information to provide regarding the military parade. (Yonhap)