Seoul, June 21 : North Korea keeps sending small groups of troops to border sentry posts for bush clearance and road maintenance, a Seoul government source said Sunday, amid concerns it could deliver on its threat of military action against South Korea. The North has sent groups of up to five soldiers with shovels and sickles to small stakeout boxes in the Demilitarized Zone separating the two Koreas. But Seoul does not see the move as a step to make good on Pyongyang's threat of military action, Yonhap News Agency quoted the source as saying. In anger over propaganda leaflets sent from the South, the North threatened to redeploy troops to the now-shuttered joint industrial complex in its border city of Kaesong and the Mount Kumgang tourist zone on its east coast, and restore border guard posts removed under a 2018 tension-reduction deal. "Guard posts and stakeout boxes are obviously facilities for military utility," the source said. "So it is natural that there are such military movements. But we are keeping close tabs on them." The military authorities here believe that an activity by at least a platoon-level number of forces could be seen as an unusual sign that requires their particular attention, the source said. The source added that there have not been any activities spotted related to the restoration of the guard posts removed under the two Korea's Comprehensive Military Agreement, which was signed in September 2018 to build mutual trust and reduce border tensions. The South Korean military is also closely watching two coastal artillery pieces on the North's border region of Gaemori, as their muzzles appeared open, spawning worries that they could be on standby for use, said the Yonhap News Agency report. "But those are things that the North often close and open. There seems to be a possibility that the muzzles were open to remove humidity or for ventilation work," the source said. Tensions between the two Koreas have continued after Pyongyang last week demolished an inter-Korean liaison office in Kaesong and warned of military action. In an unusually strong tone, the South Korean military has warned that it would respond strongly should the North launch any military provocations. /IANS