North Korea's leader, Kim Jong Un, has ordered the country's war deterrence capabilities to be strengthened and made more "practical and offensive" in response to what it called "frantic" aggression by the United States and South Korea, state media KCNA reported on Tuesday.

Kim attended an enlarged meeting of the Central Military Commission of the ruling Workers' Party of Korea on Monday to discuss "the escalating moves of the US imperialists and the South Korean puppet traitors to unleash a war of aggression," according to North Korea's state media.

US-South Korea military exercises

Meanwhile, the South Korean Defence Ministry reported that Pyongyang did not respond to its routine calls made through their direct communication channels.

Although the reasons for this lack of response to standard twice-daily calls between liaison officials were not immediately evident, experts believe that it could be a response to the US-South Korean joint military exercises.

Since March, the United States and South Korean armed forces have been performing yearly springtime drills, consisting of air and sea exercises that include a US aircraft carrier, and B-1B and B-52 bombers. It is their first extensive amphibious landing exercises in half a decade.

The suspended military communication lines are especially concerning during a time of increased tensions since they are designed to prevent accidental clashes along the two countries' maritime borders.

South Korean Unification Minister Kwon Youngse expressed disappointment during a news conference on Tuesday over North Korea's "unilateral and irresponsible attitude" toward the communication lines and also cautioned of unspecified legal consequences for its use of the Kaesong industrial assets.

South Korea warned last week it will take "necessary steps" if Pyongyang continues its unauthorized use of the joint industrial complex in the North once seen as a symbol of reconciliation.

And on Tuesday Kwon speculated that North Korea sees the current escalation of tensions as favorable to its interests, and South Korea is carefully analyzing Pyongyang's intentions.

An 'irreversible' nuclear power

Tensions in the Korean peninsula have increased considerably since last year, with North Korea increasingly testing nuclear-capable missiles despite a ban by UN resolutions.

North Korea has started the year with multiple weapons tests, comprising the launch of two intercontinental ballistic missiles and nuclear-capable underwater drones, as per state media.

Pyongyang's announcement of being an "irreversible" nuclear power last year was largely seen by experts as the end of any possibility of denuclearization discussions.

Earlier this year, Kim Jong Un had instructed the military to intensify exercises to brace themselves for a possible war.