North Korea is restricting citizens' access to its border with China, apparently in an effort to prevent news of the assassination of Kim Jong-un's half-brother from spreading.

South Korea's Chosun Ilbo newspaper reported on Thursday that North Koreans attempting to meet relatives on the border are being turned back and that additional security detachments have been deployed on the frontier.

Even people with travel permits for the border city of Sinuiju - the only place where North Koreans are permitted access to relatives living in China - were being turned away and permits were being cancelled.

Elsewhere, it was reported that jamming equipment is being used to block mobile phone calls and that new checkpoints have been set up in provinces close to the Chinese border.

South Korea, however, is using banks of loudspeakers to broadcast across the Demilitarised Zone that divides the two Koreas the news of the murder of Kim Jong-nam.

"We have made broadcasts through 34 loudspeakers along the inter-Korean border to inform North Korean soldiers and civilians that their leader, Kim Jong-un, was behind the killing of his elder half-brother, Kim Jong-nam", a military official told Yonhap news agency.