By Alex Jensen

SEOUL

North Korea held a “massive” firing drill on Tuesday, according to South Korea’s military as it monitored the North on the 85th anniversary of the foundation of its Korean People's Army.

Seoul has been on edge in expectation of a major North Korean provocation this month in line with key dates including the April 15 birthday of late national founder Kim Il-sung and the April 25 establishment of the reclusive state’s military 85 years ago.

Instead of an anticipated nuclear or long-range missile test, Pyongyang conducted a large-scale exercise involving hundreds of artillery pieces placed near its east coast on Tuesday, Yonhap news agency reported citing the South’s military.

While such weapons pose more of a threat to Seoul than the United States, North Korea also sent out a clear message to Washington, which has been bolstering its own regional capabilities amid speculation that the U.S. is mulling pre-emptive action.

“If the U.S. and warmongers run amok with a reckless pre-emptive strike, we will stage the most brutal punishment of a pre-emptive attack in the sky and land as well as at sea and from underwater without any warning or prior notice,” warned the North’s official Rodong Sinmun newspaper.

South Korea’s acting President Hwang Kyo-ahn, however, issued a counter-threat, cautioning during a Cabinet meeting that Pyongyang "would face strong measures different from what has been taken so far should it undertake another reckless provocation."

Until now, the allies have worked with the United Nations to impose sanctions against North Korea following its nuclear and ballistic missile tests.

Seoul’s Joint Chiefs of Staff said its military “is keeping a close eye” on the North’s activities, with backing from U.S. Forces Korea chief Gen. Vincent K. Brooks who added during a ceremony in Seoul that “we just stand ready”.

Around 30,000 American troops are stationed in South Korea as part of a military strategy that Pyongyang condemns as a preparation for war.