North Korea has cut off regular communications with its southern counterpart for the fifth day in a row.

South Korean government officials announced Friday that its northern neighbor has failed to respond via the two-way military liaison line normally used twice a day.

Since then, the North Korean government has continued to refuse using the phone system, likely in protest of joint military drills between the U.S., South Korea and Japan.

NORTH KOREA CUTS OFF ROUTINE CALLS WITH SOUTH KOREA AS TENSIONS RISE

"The government expresses strong regret over the North's unilateral and irresponsible attitude. We strongly warn that this will only lead the North to isolate itself and face more difficult situations," Kwon Young-se, South Korea's unification minister, said in a statement on Tuesday.

A two-way phone line connects representatives of both North and South Korea for logistical and diplomatic purposes.

It is normally used twice daily – at 9 a.m. and 5 p.m.

US AND ITS PARTNERS STAGE WARFARE DRILLS AS JAPAN, SOUTH KOREA STRENGTHEN ALLIANCE AGAINST CHINA, NORTH KOREA

South Korean officials claimed there is no defect or failure of the communication technology itself, indicating that North Korea is being willfully unresponsive.

The silence is most likely a protest of increasingly common joint military drills in the region organized between the U.S., South Korea and Japan.

North Korea state media warned last week that recent U.S.-South Korea military drills are pushing the international security situation in the region to "the brink of a nuclear war." 

NORTH KOREAN STATE MEDIA SAYS US-SOUTH KOREA MILITARY DRILLS PUSH REGION TO 'BRINK OF A NUCLEAR WAR'

The fiery remarks came a day after the U.S. military flew nuclear-capable B-52 bombers over the Korean peninsula during joint exercises with South Korea. 

"The U.S. kicked off different largest-ever joint military drills against the DPRK simultaneously despite the latter's repeated grave warnings, pushing the security situation of the Korean peninsula to the brink of a nuclear war," read an article published by the state-run Korean Central News Agency on Thursday.

Aircraft carrier USS Nimitz also participated in naval anti-submarine drills this week alongside U.S., South Korean and Japanese destroyers.