The powerful sister of North Korea's leader on Thursday denied reports by the South Korean military that Pyongyang had removed propaganda loudspeakers along the border.

In a English-language statement carried by the official Korean Central News Agency, Kim Yo Jong underscored that the South's efforts to ease tensions were worthless.

"We have never removed loudspeakers installed on the border area and are not willing to remove them," said Kim, the sister of North Korean ruler Kim Jong Un.

Since his election in June, South Korean President Lee Jae Myung has vowed to reach out to the nuclear-armed North and pursue dialogue without preconditions, in a reversal from his hawkish predecessor.

South Korea had been blaring K-pop and news reports to the North in response to Pyongyang transmitting bizarre, unsettling noises along the border that had become a major nuisance for South Korean locals.

The two countries had halted propaganda broadcasts along the demilitarised zone, Seoul's military said in June after Lee's election.

South Korea's defence ministry said on August 5 it had begun removing loudspeakers from its side of the border as "a practical measure aimed at helping ease tensions with the North".

In her Thursday statement, Kim dismissed such gestures.

"Recently, the ROK has tried to mislead public opinion by saying that its 'goodwill measures' and 'appeasement policy' are meeting a response, as well as to create public opinion that the DPRK-ROK relations are being 'restored'", she said, referring to the two Koreas by the abbreviations of their formal names.

"We have clarified on several occasions that we have no will to improve relations with the ROK... and this conclusive stand and viewpoint will be fixed in our constitution in the future," Kim said.

Her statement came as South Korea and the United States prepare to hold annual joint military drills aimed at containing the North, from August 18 to 28.

"Whether the ROK withdraws its loudspeakers or not, stops broadcasting or not, postpones its military exercises or not and downscales them or not, we do not care about them and are not interested in them," Kim said.

"I am confident that Seoul's policy towards the DPRK remains unchanged and can never change."

The two countries technically remain at war because the 1950-53 Korean War ended in an armistice, not a peace treaty. (AFP)