On Thursday, South Korea’s army conducted its largest-ever artillery drills near the tense border with North Korea, risking an escalation of tensions on the Korean Peninsula.

Dozens of military units along the border on Thursday deployed some 300 artillery systems that simultaneously fired shells in multiple directions, according to an army official, who spoke on condition of anonymity to Military.com.

South Korea’s front-line army units have engaged in numerous live-fire drills over the years, but the number of artillery mobilized in Thursday’s drill is the highest on the Korean peninsula to date, and simultaneous firing from all major front-line areas constitutes a stark departure from previous exercises, according to the army official.

North Korea has long stated that it is under threat of a nuclear attack from the United States. Washington has undertaken the practice of flying B-2 and B-52 bombers over the country, sending a stern message to Pyongyang that the United States stands with South Korea. The North has also said that they view the escalation of war games by the United States as a "dress rehearsal" for a full-scale invasion.

In response to being added to the existing sanctions against Pyongyang, Kim Jong-un, the country’s supreme leader, declared war on the United States two weeks ago.

Pyongyang in recent months has not only escalated its rhetoric, but also brandished its weapons systems. North Korea has engaged in numerous tests of mid-range ballistic missiles in recent months, with increasing sophistication according to Western defense analysts. The country announced Wednesday that the Yongbyon nuclear facility, used for creating weapons-grade nuclear material, had been reactivated after having been suspended in 2007 as part of an agreement forged in six-party talks.

The potential for hostilities faces an additional upgrade, with Thursday marking the 40th anniversary of the 1976 "ax murder incident" in which two US soldiers were hacked to death by North Koreans during a border area clash over US efforts to trim a tree. Thursday also marks the one-year anniversary of an artillery exchange on the peninsula, following two South Korean soldiers being maimed by land mine explosions.