North korea
North Korean leader Kim Jong Un (center) smiles as he guides a test fire of a new multiple launch rocket system in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang, March 4, 2016. REUTERS/KCNA

North Korea's Kim Jong Un will most likely order the launch of a Musudan intermediate-range ballistic missile (IRBM) instead of a long-range one, South Korean military officials said Monday. The news comes hours after U.S. President Donald Trump and South Korean Acting President Hwang Kyo-ahn vowed to strengthen their defenses to combat North Korea's nuclear threat.

"There are no signs of an imminent test firing of an intercontinental ballistic missile (ICBM) by North Korea. But we are closely monitoring any new military activities in the country as it could launch an IRBM at any time if leader Kim Jong Un gives the order," an official at the South Korean defense ministry said, according to Yonhap News Agency.

During the New Year's Day address, Kim announced that the country has entered the final stage of preparations to test-fire an ICBM, capable of carrying a nuclear warhead.

On Sunday, the White House released a statement saying that Trump and Hwang spoke over the phone, where they discussed North Korea's continuous threats, and also the upcoming visit by the new U.S. defense secretary to Japan and South Korea.

"President Trump reiterated our ironclad commitment to defend (South Korea), including through the provision of extended deterrence, using the full range of military capabilities," the White House said in the statement.

The U.S. and South Korea have agreed to deploy a Terminal High Altitude Area Defense (THAAD) system in order to protect against North Korea's growing nuclear and ballistic capabilities.

Last week, South Korean and U.S. sources claimed that North Korea has placed two ICBMs on mobile launchers, giving rise to speculation that the test could come earlier than expected.

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.