North Korea said it fired more than 130 artillery shells into the sea off its east and west coasts on Monday after detecting military drills across the border in the South. Some of the shells landed in a buffer zone near the sea border in what Seoul said was a violation of a 2018 inter-Korean agreement to reduce tensions.

The South Korean military sent several warning communications to the North over the firing, the ministry of defence said in a statement. North Korea’s military conducted its firing after detecting dozens of “projectiles” fired in the South near the shared border, state news agency KCNA reported, citing a spokesperson of the General Staff of the Korean People’s Army.