The missile fired from the North’s western Hwanghae province flew toward the water off the country’s east coast, the South’s Joint Chiefs of Staff said in a statement.

South Korean military officials were analyzing what type of missile it was and how far it flew, according to Seoul’s Defense Ministry.

North Korea routinely conducts missile and other weapons tests, but the latest launch came after North Korea warned of unspecified “physical counter-actions” against a U.S. plan to deploy an advanced missile defense system in South Korea by the end of next year.

Seoul and Washington officials said they need the Terminal High-Altitude Area Defense, or THAAD, system to better cope with what they call North Korea’s increasing military threats. North Korea called the system a provocation that it says is only aimed at bolstering U.S. military hegemony in the region.

On July 19, North Korea fired three ballistic missiles into the sea, according to Seoul defense officials. The North’s state media later confirmed that it fired ballistic rockets carrying trigger devices for nuclear warheads as part of simulated pre-emptive atomic attacks on South Korea.

North Korea is expected to perform more weapons launches in coming weeks to protest annual U.S.-South Korean military drills that begin later this month. North Korea describes the drills as an invasion rehearsal.

North Korea is pushing to manufacture a warhead small enough to be placed on a long-range missile that can reach the continental U.S., but South Korean defense officials say the North doesn’t yet have such a miniaturized warhead. Some civilian experts, however, believe the North has the technology to put warheads on shorter-range missiles that can strike South Korea and Japan.