SEOUL, South Korea >> North Korea on Saturday fired several unidentified short-range projectiles into the sea off its eastern coast, the South Korean Joint Chiefs of Staff said, a likely sign of Pyongyang’s growing frustration at stalled diplomatic talks with Washington meant to provide coveted sanctions relief in return for nuclear disarmament.

South Korea’s military has bolstered its surveillance in case there are additional weapons launches, and South Korean and U.S. authorities are analyzing the details. If it’s confirmed that the North fired banned ballistic missiles, it would be the first such launch since the North’s November 2017 test of an intercontinental ballistic missile. That year saw a string of increasingly powerful weapons tests from the North and a belligerent response from President Donald Trump that had many in the region fearing war.

The South initially reported Saturday that a single missile was fired, but later issued a statement that said “several projectiles” had been launched and that they flew up to 200 kilometers (125 miles) before splashing into the sea toward the northeast. Experts say the North may increase these sorts of low-level provocations to apply pressure on the United States to agree to reduce crushing international sanctions.

The launch comes amid a diplomatic breakdown that has followed the failed summit earlier this year between Trump and North Korean leader Kim Jong Un over the North’s pursuit of nuclear bombs that can accurately target the U.S. mainland. The North probably has viable shorter range nuclear armed missiles but still needs more tests to perfect its longer-range weapons, according to outside analysts.

White House Press Secretary Sarah Sanders said in a statement that the United States was aware of North Korea’s actions and would continue to monitor the situation.

North Korea wants widespread sanctions relief in return for disarmament moves that the United States has rejected as insufficient. In a sign of Pyongyang’s growing frustration, it has recently demanded that U.S. Secretary of State Mike Pompeo be removed from nuclear negotiations and criticized national security adviser John Bolton. North Korea said last month that it had tested a new type of unspecified “tactical guided weapon.”

During the diplomacy that followed the North’s weapons tests of 2017, Kim Jong Un said that the North would not test nuclear devices or ICBMs. These short-range projectiles don’t appear to violate that self-imposed moratorium, and may instead be a way to register Kim’s displeasure with Washington without having the diplomacy collapse.

The South’s presidential Blue House had no immediate comment on the launches. The country’s liberal president, Moon Jae-in, has doggedly pursued engagement with the North and is seen as a driving force behind the two summits between Trump and Kim.

Japan’s Defense Ministry said the projectiles weren’t a security threat and didn’t reach anywhere near the country’s coast. Japan will likely avoid any harsh response as Prime Minister Shinzo Abe seeks to secure his own summit with Kim.