Seoul, April 8 : North Korea remained unresponsive to regular contact via a military hotline for the second day on Saturday, military officials said. The North did not respond to the regular 9 a.m. opening call between the two sides after daily calls through the cross-border liaison line and the military hotline the previous day went unanswered, Yonhap News Agency quoted the officials as saying. The two Koreas typically hold phone calls twice a day in the morning and in the afternoon using the joint liaison office channel and their military channel. While the liaison office channel operates only on weekdays, the military channel also conducts calls on weekends. "Regular calls aren't being made due to an unspecified reason from the North's side," a military official said. "We will monitor the situation, including the possibility of a (technical) problem in the North's line." The suspension comes amid heightened tensions on the Korean Peninsula in the wake of North Korea's recent weapons tests in protest of joint military drills between South Korea and the US. Earlier in the day, the North's state media reported that the country staged an underwater detonation test of its Haeil-2 nuclear-capable attack drone earlier this week. /IANS