North Korean leader Kim Jong Un threatened tit-for-tat nuclear attacks if Pyongyang was "provoked with nukes," state media said Thursday.

Kim's warning follows a meeting between South Korea and the United States last week in Washington, where they discussed nuclear deterrence in the event of conflict with the North.

The meeting's agenda included "nuclear and strategic planning," and the allies reiterated that any nuclear attack by Pyongyang on the United States or South Korea would result in the end of the North Korean regime.

But Kim told his military's missile bureau "not to hesitate (launching) even a nuclear attack when the enemy provokes it with nukes," Pyongyang's official Korean Central News Agency said Thursday.

Washington, Seoul and Tokyo released a statement shortly afterward, urging the nuclear-armed country to "stop conducting further provocations and accept our call for engaging in substantive dialogue without preconditions."

The three countries have ramped up defense cooperation in the face of a record-breaking series of weapons tests by Pyongyang this year, and on Tuesday activated a system to share real-time data on North Korean missile launches.

On Monday, the North launched its most powerful intercontinental ballistic missile, the Hwasong-18, later describing it as "a warning countermeasure" against what it described as persistent acts of "military threat" by Washington and its allies.

Last week, a U.S. nuclear-powered submarine arrived in the South Korean port city of Busan, and on Wednesday, Washington flew its long-range bombers in drills with Seoul and Tokyo.

The North has recently stressed that the "Korean peninsula is in a state of war by law" and that "strategic assets" deployed by Washington in the South will be "the first targets of destruction."

In October, when a U.S. B-52 bomber capable of carrying nuclear weapons took part in the first joint aerial drills conducted by Seoul, Tokyo and Washington, Pyongyang described the exercise as "the intentional nuclear war provocative moves of the U.S."

Pyongyang sees drills by the United States and its allies as rehearsals for invasion and has long justified its blitz of missile launches as necessary "countermeasures."

Seoul's defense minister has been making unusually fiery remarks of late and last week warned that Pyongyang would face a "hell of destruction" if it engaged in any "reckless" action that "destroys peace."

The two Koreas are at a "peak of escalating rhetoric and pre-emptive strike threats," Yang Moo-jin, president of the University of North Korean Studies in Seoul, told AFP.

The latest developments "clearly reflect the seriousness of the situation and the current (turbulent) state of affairs on the Korean Peninsula," he added.

Invasion preparations

Pyongyang last year declared itself an "irreversible" nuclear power and has repeatedly said it will never give up its nukes program, which the regime views as essential for its survival.

In a separate statement Thursday, Kim's powerful sister, Kim Yo Jong, slammed the United Nations Security Council for convening a session to discuss the North's latest ICBM launch, arguing it was a demonstration of Pyongyang's inherent right to self-defense.

"The ceaseless military drills of the U.S. and its vassal forces (remind) one of the overall preparations for invasion under the pretext of deterring threats from someone," she said, according to KCNA.

"And the frequent appearance of the U.S. nuclear weapons clearly (aimed) at the DPRK ... is the root cause of escalating the regional situation," she added, using the acronym for the North's official name.

Pyongyang's launch of a military spy satellite last month, which it claimed quickly began providing images of U.S. and South Korean military sites, further damaged inter-Korean ties.

The launch fractured a military agreement between the Koreas established to de-escalate tensions on the peninsula, with both sides then ramping up security along the Demilitarized Zone (DMZ) that separates them.