Seoul, April 9 : North Korea did not answer routine calls from South Korea via a military hotline for the third day in a row Sunday for unclear reasons, officials said. The two Koreas are supposed to hold calls twice a day -- once in the morning and the other in the afternoon -- via military and liaison hotlines set up across the border, but the North stopped answering calls from the South on Friday afternoon, Yonhap News Agency reported. On Sunday, the South made military hotline calls to the North at 9 a.m. and 4 p.m., but both went unanswered again, according to the defence ministry officials. Calls through the liaison hotline do not take place on weekends. It is unclear why the North is refusing to answer the calls. But 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. /IANS