SEOUL - North Korea has covered the entrance to a tunnel at its nuclear test site in an apparent effort to avoid satellite monitoring ahead of a widely expected detonation, a report said Friday. The Punggye-ri site, which has three tunnel entrances and multiple support buildings, has been closely monitored by US, South Korean and Japanese intelligence since North Korea ramped up its test threats just over a week ago. “Analysis showed a camouflage net looking like a roof was placed on the tunnel entrance,” Yonhap News Agency cited a senior South Korean government source as saying. “The move seems to be aimed at keeping nuclear test preparations - now near their completion - from being exposed outside,” the source said.