North Korea has refused to engage with South Korea via their regular communication for the fourth straight day.

According to the unification and defense ministries on Monday, calls through the liaison office and military hotlines at 9 a.m. were not made due to the North's unresponsiveness.

Unification ministry spokesperson Koo Byoung-sam said in a briefing that for now, the presumption is that the North unilaterally cut off communication. He said the government will look into response measures, expecting to issue an official position soon. 

Defense ministry spokesperson Jeon Ha-kyu said the ministry is open to all possibilities including irregularities in the communication line. 

The two Koreas typically make daily contact twice, with the liaison office making calls at 9 a.m. and 5 p.m. and the military doing so at 9 a.m. and at 4 p.m.

While the reason behind the lack of response since last Friday remains unclear, it is speculated that it is an apparent retaliation against Seoul and Washington's joint military drills and South Korea's published report on the North's human rights abuses.