North Korea on Sunday launched its fourth short-range projectile into waters off its east coast, marking the latest provocation from Pyongyang.

South Korean officials had called the weapons tested “short-range guided missiles.”

On Sunday, they began referring to what was launched over the last two days as “projectiles,” saying they may have included not only the modified KN-02 short-range guided missile but also rockets from the new multiple launcher, The New York Times reported.

UN Secretary General Ban Ki-Moon said that he was “very worried over North Korea’s provocative action,” and urged the regime to cease all provocations.

The move comes after recent months of increased hostilities, as North Korea tested long-range missiles and threatened the United States and South with nuclear war.

Pyongyang conducted a third nuclear test in February, spurring a new round of UN sanctions.

Earlier this month, Pyongyang sentenced an American, Kenneth Bae, to 15 years’ hard labor for allegedly plotting to overthrow the regime, prompting the State Department to demand his immediate release.