On Saturday, North Korea launched two short-range ballistic missiles into the sea off its east coast, just hours before South Korea performed a massive military demonstration with stealth planes and its own missiles.

Pyongyang’s fourth launch in a week comes amid a flurry of military drills by regional countries, including coordinated anti-submarine operations by the fleets of South Korea, the United States, and Japan on Friday.

U.S. Vice President Kamala Harris visited the region this week, meeting with South Korean President Yoon Suk-yeol in Seoul on Thursday.

The rival Koreas are in a regional arms race that has seen a major increase of weapons and military spending.

Marking South Korea’s 74th Armed Forces Day, Yoon condemned what he called recent military provocations by the North and vowed to strengthen joint military drills with the United States.

“The government will further strengthen the Korea-U.S. joint exercises, will respond strongly to North Korean provocations and threats by showing them the ‘Alliance in Action’,” Yoon said in a televised speech.

He and military officials observed a major show of advanced weaponry, including multiple rocket launchers, ballistic missiles, main battle tanks, drones and F-35 fighter aircraft, among other systems.

The U.S. military demonstrated fighter jets and attack aircraft. Images of the event showed Yoon saluting from the back of a convertible car while driving by rows of tanks and other weapons.

He has said his country’s conventional weapons are key to deterring the North, and Seoul has also been seeking more major arms sales around the world.

According to a July assessment from Japan’s Defense Ministry, the North has started launching short-range missiles with low and erratic trajectories, which have been spotted since May 2019 and are presumably meant for greater war-fighting efficacy.

The North has been sanctioned by the United Nations Security Council for its ballistic missile and nuclear tests. Such measures are viewed as an infringement on Pyongyang’s sovereign right to self-defense and space development.

The North has finalized preparations for a nuclear test, potentially opening a window between China’s Communist Party Congress this month and the November midterm elections in the United States, South Korean legislators warned on Wednesday.