North Korea advanced its missile attack capabilities by successfully conducting a high-powered, solid-fuel rocket engine test, the reclusive state said Thursday. Following the announcement, South Korean President Park Geun-hye ordered security forces to strengthen their vigilance against North Korea's "reckless provocation."

North Korean leader Kim Jong Un reportedly attended the successful testing of a "large-output solid fuel rocket engine," which made an "earth-shaking" sound. He said that the test will enhance missile capability and help "strike great horror and terror into the hearts of the enemies," North Korea's state news agency KCNA reported Thursday. However, it was unclear when North Korea conducted the test.

South Korea's Defense Ministry said Thursday it needs to analyze the statement, the Associated Press reported.

“[The Defense Ministry] believes that North Korea is at a stage of developing solid fuel [for missiles]. ... We believe it is attempting to boast the progress of its nuclear and missile programs,” ministry spokesman Moon Sang-gyun said, according to local media reports.

North Korea's announcement came as it was angrily responding to the ongoing joint military drills by South Korea and the United States. The military exercises began after North Korea conducted its fifth nuclear test on Jan. 6 and launched its long-range rockets on Feb. 7, resulting in an escalation of tensions between the two Koreas.

On Monday, Pyongyang also fired five short-range projectiles off its east coast, three days after it launched its medium-range ballistic missile into the Sea of Japan, Seoul officials reportedly said.

Kim Jong Un’s regime recently threatened missile launches and nuclear tests after the United Nations Security Council voted to place sanctions against the country.