South Korean marines responded by conducting afternoon live-fire drills in the Yellow Sea, South Korea’s Defense Ministry said in a news release.

Yeonpyeong, located less than 10 miles from the North Korean coastline, was the site of a deadly North Korean surprise attack in 2010, when Pyongyang launched scores of shells. Four people, including two South Korean marines serving on the island, were killed.

Col. Lee Sung-jun, a spokesman for the South’s armed forces, demanded the North “immediately cease” actions that increase tensions, reading aloud a prepared statement.

Hundreds of civilians living on Yeonpyeong had entered bomb shelters, an official at the county office said. A total of 2,100 people live there, the official said, including the family members of the marines serving on the garrison there. The 4,800 residents of Baegnyeong had also been ordered into bomb shelters, a South Korean official there said.

The sheltering orders were lifted at 3:45 p.m. local time, the two officials said.

The development reflects North Korea’s goal of raising regional tensions, Lee said. “The responsibility for this heightened state of tensions lies completely with North Korea,” he added.

North Korean leader Kim Jong Un has consistently vowed to continue upgrading his nuclear arsenal and military since rising to power more than a decade ago. Most recently, Kim said his soldiers would accelerate efforts to “subdue the entire territory of the South in case of war,” using “all physical means” including nuclear weapons, in a statement published by state media late last year.

The shelling incident comes as a South Korean army brigade conducted a days-long exercise this week with elements of the U.S. Army’s 2nd Infantry Division, according to state broadcaster KBS. The U.S. military maintains 28,500 troops in the South, primarily to deter North Korea, and conduct routine training and field exercises with South Korean soldiers. The North regularly denounces those drills.