South Korea and the United States on Monday began their annual two-week joint war exercise to test and improve their joint defense posture against North Korea amid the North‘s stronger-than-usual threats against the drill.

The computer-aided Ulchi Freedom Guardian kicked off for a 12-day run, mobilizing some 50,000 South Korean forces and 30,000 U.S. servicemen, including some 3,000 from its homeland and other overseas bases.

With the training expected to include diverse defense drills to curb North Korea’s possible provocations, this year will be the first time for the allies to implement their customized deterrence plan against Pyongyang‘s nuclear threats and weapons of mass destruction, according to the ministry.

The bilateral strategy, drawn up during their defense ministerial meeting last year, delineates how they should work together to deter both wartime and peacetime aggression from Pyongyang, from saber-rattling to the actual use of force.

The drill came amid a series of heightened threats from the communist North, though it has long balked at the annual drills and other similar joint maneuvers, claiming they are a prelude to war despite Seoul and Washington’s argument that they are defensive in nature.

Dubbing the Seoul-Washington drills an “unpardonable military provocation” that brings the situation on the Korean Peninsula to “a hair-trigger crisis and casts dark clouds of nuclear war,” the North on Monday vowed to deal “a merciless blow”

“The army and people of the DPRK love peace but never beg for it. They will deal a merciless blow to those encroaching upon the sovereignty of the DPRK even a bit,” its major newspaper Rodong Sinmun said. DPRK is the acronym for the Democratic People‘s Republic of Korea, the North’s official name.

“All the armed forces participating in the joint military exercises and their bases are becoming targets of our powerful ultra-modern, ultra-precision strike means, including strategic and tactical rockets.”

Pyongyang‘s foreign ministry also issued a statement, blasting the U.S. for its “arms buildup in Northeast Asia.”

“North Korea will take self-defensive counteractions on an annual and regular basis and take steps at a higher level in future that no one will be able to predict” as long as the “nuclear war maneuvers go on to stifle Pyongyang,” the ministry said.

On Sunday, North Korea also vowed to launch “the strongest, most merciless pre-emptive attacks of our own style,” in a statement issued by an unidentified spokesman for the General Staff of the Korean People’s Army.

In response, Seoul‘s defense ministry expressed deep regret, vowing a “merciless counterattack” in case of any provocations.

“During the UFG period, we will further strengthen reconnaissance activities to maintain a tighter defense posture against North Korea,” a ministry official said, asking not to be named.

In recent months, North Korea has employed its signature, two-tier strategy of engagement and pressure. In the latest in a series of saber-rattling moves, the North fired five short-range rockets into the East Sea on Thursday, while its leader Kim Jong-un sent a wreath marking the fifth anniversary of the death of South Korea’s former President Kim Dae-jung on Sunday.

Along with the war exercise, the South Korean government kicked off a separate four-day emergency exercise earlier in the day.

The annual local drill, involving administrative bodies and public employees nationwide, is designed to examine the government‘s readiness for dealing with military provocations from the North and potential terrorist attacks.

The Koreas remain technically at war because the 1950-53 Korean War ended in an armistice. About 28,500 U.S. soldiers are stationed in South Korea. (Yonhap)