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."

North Korea could choose to fire more missiles with longer ranges in coming weeks to ramp up its pressure on the United States to come up with a roadmap for nuclear talks by the end of this year, said Nam Sung-wook, a professor at Korea University.

"North Korea wants to say, 'We have missiles and nuclear weapons to cope with (U.S.-led) sanctions,'" said Nam. "They can fire short-range missiles a couple more times this month, and there is no guarantee that they won't fire a medium-range missile next month."

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.

After the launches, South Korea's presidential national security adviser, the defense minister and the intelligence chief gathered at the presidential Blue House to monitor the situation, according to the Blue House. It said South Korea and the United States are closely sharing information about the launches.

South Korea'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.

South Korean Foreign Minister Kang Kyung-wha talked by phone with Pompeo about the North Korean launches, Kang's ministry said in a statement. The ministry also said that South Korea's chief nuclear envoy, Lee Do-hoon, had a telephone conversation with Stephen Biegun, the U.S. special representative for North Korea who is scheduled to travel to Seoul next week for talks.

The United States and South Korea are analyzing North Korea's short-range missile launches while "carefully responding" to Pyongyang's action, according to South Korean Foreign Ministry statement following telephone talks between U.S. Secretary of State Mike Pompeo and his counterpart in Seoul.

Later Saturday, South Korean Foreign Minister Kang Kyung-wha also talked by phone with Japanese Foreign Minister Taro Kono and they agreed to keep coordinating while also "carefully responding" to the launches.

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.

Japan's Foreign Ministry said Kono, who is currently visiting Angola, and Pompeo also talked for about 10 minutes Saturday and confirmed the two sides will share information on the development and stay in close contact.

The two ministers also agreed to cooperate with South Korea. Japan's Defense Ministry says 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 Jong Un.