North Korea on Tuesday fired a ballistic missile into the Sea of Japan, the South Korean military said, according to The Guardian. South Korea said that the missile seemed to have been launched from asubmarine, CNN reported.

The missile was launched from Sinpo, a major naval shipyard in North Korea, according to AFP. Submarines have previously been seen at the facility.

“Our military is closely monitoring the situation and maintaining readiness posture in close cooperation with the United States, to prepare for possible additional launches,” South Korea’s Joint Chiefs of Staff said, according to Reuters.

North Korea has undertaken a series of missile tests recently.

On September 15, the country had fired two missiles off its eastern coast. A few days before that, North Korea tested its new long-range cruise missile that reportedly had the potential to hit Japan.

International law prohibits North Korea from testing nuclear weapons or ballistic missiles.

After Tuesday’s launch, South Korea’s national security council convened an emergency meeting, while Japan described the test as “regrettable”, Reuters reported.

Meanwhile, the United States said it wanted to hold talks with North Korea, AFP reported.

“We will seek diplomacy with the DPRK [Democratic People’s Republic of Korea] to make tangible progress that increases the security of the United States and our allies,” US Special Representative on North Korea Sung Kim said, according to AFP.

Sung added that the US had no “hostile intent” towards North Korea and hoped to hold a meeting with its representatives without conditions.