North Korea Missile
An underwater test-firing of a strategic submarine ballistic missile is seen in this undated photo released by North Korea's Korean Central News Agency in Pyongyang, April 24, 2016. KCNA via Reuters

Just a day after North Korea conducted a failed missile test, South Korea has increased vigilance over Pyongyang suspecting more missile tests in the coming weeks, Seoul's defense officials and experts said Thursday. Kim Jong Un's regime has been ramping up its nuclear program and testing ballistic missiles despite receiving tough sanctions.

"Chances are high that North Korea may soon take additional provocative steps," a senior defense ministry official said, according to Yonhap News. "A key concern is whether it will test-fire an intercontinental ballistic missile (ICBM) or conduct a nuclear test."

South Korea's military is closely monitoring Pyongyang's activity, the official said, adding that the military is on standby for any emergency situation.

North Korea’s latest missile test from its east coast failed after the rocket exploded within seconds of launch, the U.S. Pacific Command and the South Korean Defense Ministry said. It is unclear what type of missile was tested Wednesday.

Read: North Korea Threatens 'Actual War' Over US-South Korea Exercises

Earlier this month, North Korea fired four ballistic missiles into the sea off Japan's northwest coast on March 12 amid escalating tensions with South Korea and Japan. The missiles, which were launched from the Dongchang-ri long-range missile site in North Pyongan Province, flew about 620 miles before hitting the Sea of Japan.

North Korea claims that it fired the missiles in retaliation to U.S.-South Korea joint military drills, which the reclusive country sees as provocations of war in the Korean Peninsula.

Earlier this month, satellite images of North Korea’s Punggye-ri test site obtained by 38 North, a website run by the U.S.-Korea Institute at Johns Hopkins University in Washington, showed continued activities at the North Portal.

Kim Dong-yup, a professor at the Institute for Far East Studies of Kyungnam University, told Yonhap News: "North Korean troops will stage a large-scale exercise to wrap up the winter training at an on-site inspection of leader Kim Jong-un. It's expected to fire various types of missiles this time, including FROG-7 artillery, KN-02 short-range and Scud missiles."

North Korea has boasted it is developing a missile that could carry a nuclear warhead to the U.S. West Coast, but South Korea and Japan remain the most likely targets.

South Korean military officials also believe that North Korea is likely to fire an intermediate-range ballistic missile or conduct its sixth nuclear test to commemorate the 105th birth anniversary of the North's founder Kim Il Sung on April 15.