North Korea's leader Kim Jong Un speaks at the Capella Hotel on Sentosa island in Singapore on June 12, 2018.

North Korea fired two unidentified projectiles into the sea on Thursday, South Korea's military said, the first launches in more than two months as North Korean and U.S. officials work to restart nuclear diplomacy.

The South's Joint Chiefs of Staff said the projectiles were fired from the eastern coastal town of Wonsan and flew 430 kilometers (267 miles). It wasn't immediately known what type of projectiles North Korea fired. But in the past, such launches have involved missiles or artillery.

Some observers say the North could intend to show the U.S. and others what would happen if diplomacy fails. Recently, North Korea was ramping up pressure on the U.S. ahead of the possible resumption of nuclear talks.

North Korea is desperate to win sanctions relief, but U.S. officials have maintained North Korea must first take significant steps toward nuclear disarmament.

A senior U.S. official said the Trump administration was aware of the reports of a "short-range projectile launched from North Korea." The official, who spoke on condition of anonymity to provide a response, said the administration had no further comment at this time.

It was the first such launches since Seoul said North Korea fired three short-range missiles off its east coast in early May. Many experts said at the time that those missiles bore a strong resemblance to the Russian-designed Iskander, a short-range, nuclear-capable ballistic missile that has been in the Russian arsenal for more than a decade.

South Korea's military said it and the U.S. military were analyzing details of the launches. South Korea said it was monitoring possible additional launches by North Korea.

During a third summit at the Korean border late last month, U.S. President Donald Trump and North Korean leader Kim Jong Un agreed to resume nuclear negotiations, which had been deadlocked since their second summit in Vietnam in February ended without an agreement because of disputes over U.S.-led sanctions.

North Korea said last week that it may lift its 20-month suspension of nuclear and missile tests to protest expected military drills between the United States and South Korea that Pyongyang says are a rehearsal of an invasion.

Thursday's launches won't end that weapons test moratorium, which applies to firing long-range missiles capable of reaching the mainland U.S.

On Tuesday, North Korean state media said Kim inspected a newly built submarine and ordered officials to further bolster the country's military capabilities. The Korean Central News Agency said the submarine's operational deployment "is near at hand."

After analyzing North Korea-dispatched photos of the submarine, experts said the submarine likely has three launch tubes for missiles. South Korean government documents say North Korea has about 70 submarines, but analysts say they mostly have a single launch tube.

The construction of such a new submarine suggests North Korea has been increasing its military capability despite nuclear diplomacy that it began with the United States early last year.