SEOUL, South Korea (AP) — South Korean and U.S. troops have been conducting live-fire exercises this week to hone their ability to respond to potential “Hamas-style surprise artillery attacks” by North Korea, South Korea’s military said Friday.

The two forces regularly conduct live-fire and other training, but this week’s drills come after Hamas’ Oct. 7 assault on Israel raised security jitters in South Korea, which shares the world’s most heavily fortified border with rival North Korea.

Experts say the North’s forward-deployed long-range artillery guns can fire about 16,000 rounds per hour in the event of a conflict, posing a serious threat to Seoul, which is about 40-50 kilometers (25-30 miles) from the border.

The three-day firing exercises, which began Wednesday, involved 5,400 South Korean and U.S. soldiers, 300 artillery systems, 1,000 vehicles and air force assets, according to South Korea’s military.

In a simulated response to “the enemy’s (possible) Hamas-style surprise artillery attacks,” the exercises practiced strikes designed to “remove the origins of the enemy’s long-range artillery provocations at an early date,” South Korea’s Ground Operations Command said in a statement.

North Korea didn’t immediately react to the drills. It typically views major U.S.-South Korean military training as invasion rehearsals and responds with missile tests.

South Korea and the United States have been expanding their regular military drills in the face of North Korea’s advancing nuclear program. Since last year, North Korea has carried out more than 100 missile tests, some of them simulated nuclear attacks on South Korea and the U.S.