South Korea slammed North Korea on Thursday for denouncing the joint military exercises by Seoul and Washington, scheduled for next month, as a rehearsal for an invasion. An official from Seoul's unification ministry told Yonhap News Agency that Pyongyang should end its nuclear threats. 

"If North Korea wants to see an improvement in the inter-Korean ties and peace on the Korean Peninsula, it should stop its bellicose rhetoric and take the path toward denuclearization and changes," the official said, according to Yonhap. On Wednesday, North Korea threatened to take actions over the upcoming military drill, which the reclusive country thinks will lead to "shameful destruction." North Korean leader Kim Jong Un believes that South Korea and the U.S. are using the joint drills to prepare for a nuclear war.

Despite receiving sanctions from the United Nations over its nuclear advancements, North Korea says that its development of nuclear weapons is a deterrent against what the country believes to be Washington's hostile policy toward it.

The South Korean ministry official also reportedly said that the North's statement about the March drill came sooner than they expected.

"The level of North Korea's bellicose rhetoric seems to be similar to that of last year, but North Korea's comments on pre-emptive strikes warrant close attention," he added.

The comments come as U.S. Defense Secretary James Mattis arrived Thursday in Seoul to reiterate Washington's commitment toward strengthening the military in the face of North Korea's growing threats.

The defense ministry said that Mattis headed to the U.S. Forces Korea headquarters in Yongsan, Seoul, after arriving at Osan Air Base in Pyeongtaek, 45 miles south of Seoul. He is scheduled to attend a dinner event arranged by Defense Minister Han Min-koo after meetings with Acting President and Prime Minister Hwang Kyo-ahn and National Security Office chief Kim Kwan-jin, Yonhap reported, citing sources. 

Mattis will also hold a separate meeting Friday with Han and Foreign Minister Yun Byung-se to discuss the North's nuclear and missile threats.

Meanwhile, the U.S. and South Korea have agreed to deploy a Terminal High Altitude Area Defense (THAAD) system amid North Korea's growing nuclear and ballistic capabilities.

In recent months, North Korea has carried out several ballistic missile tests and ramped up its nuclear program, increasing tensions with the West and its southern neighbor. During his New Year address, Kim claimed that the country has entered the final stage of preparations to test-fire an intercontinental ballistic missile (ICBM) capable of carrying a nuclear warhead.