North Korea angrily hit back at allegations citizens who failed to appear sincere in the mourning of leader Kim Jong-Il were being rounded up and sentenced to hard labour.

Some media outlets in the South have claimed North Koreans who did not participate in organised public mourning, failed to cry, or did not appear genuine, have been sentenced to at least six months in labour camps.

But Pyongyang's official Korean Central News Agency (KCNA) on Saturday said such "misinformation" touched off "towering resentment" among North Koreans, denouncing those who spread the allegations as "pitiable human scum".

"The group of traitors hell-bent on the anti-DPRK (North Korea) campaign could hardly understand the weight and sincerity of the tears shed by the service personnel and people of the DPRK," KCNA said.

The reports originated on Daily NK, an Internet website run by opponents of North Korea, which said it had learned the information from a source in the isolated communist state's northeastern province of North Hamkyong.

In recent weeks the North has accused the South's government of showing disrespect during the mourning period for Kim, who died on December 17 and was succeeded by his son Jong-Un.

Relations have been icy since the South accused the North of responsibility for two deadly cross-border incidents in 2010.

On Thursday, the North's state Committee for the Peaceful Reunification of Korea said Lee's government had escalated confrontation and staged a smear campaign.

It said the South Korean military was put on alert following the announcement of Kim's sudden death and accused the Seoul government of "levelling the gun at the fellow countrymen shedding tears in great grief".