North Korea continues to escalate tensions in the region with the launch of several cruise missiles towards the sea, according to South Korea’s Joint Chiefs of Staff. The launches come as the South Korea-US military training draws to a close, and the US is reportedly preparing to send an aircraft carrier to the region for further drills.

North Korea has denounced the joint training as an invasion rehearsal and has used the drills as a reason to increase weapons testing activity. Experts assert that leader Kim Jong Un’s aim is to build up his weapons’ arsenal in order to gain concessions while burnishing his image as a strong leader in the face of domestic economic difficulties.

Cruise missile tests are not prohibited by multiple U.N. Sanctions, but the technology is viewed as a serious threat by North Korea’s neighbors, as the missiles can fly at a lower altitude to evade radar detection.

There are concerns that the missiles could be used to strike US aircraft carriers or other large enemy ships if a conflict were to arise. The North has said that some of its ballistic and cruise missiles are “strategic” weapons, indicating it aims to arm them with nuclear warheads.