A hotline telephone at the Seoul branch of the joint inter-Korean liaison office / Courtesy of Ministry of Unification

North Korea was not responding to daily contact via an inter-Korean liaison line Tuesday, South Korea's unification ministry said hours after Pyongyang fired an intermediate range ballistic missile into the Pacific.

"The North had not answered an opening call through an inter-Korean liaison communication line as of 9 a.m., while the military hotline was in normal operation," a ministry official said, adding the government is trying to find out the reason amid the possibility of a technical problem.