North Korea has fired two unidentified projectiles into the sea early Saturday morning local time.
The projectiles were fired "at dawn from Hamheung area into the East Sea," a spokesperson for South Korea's Joint Chief of Staff said in a statement. "Our military is following up with the surveillance over possibility of additional launches as well as maintaining our military preparedness."
The Pentagon and White House did not immediately respond to CNBC's request for comment.
Later, press secretary Stephanie Grisham said President Donald Trump has been briefed on the matter.
A senior administration official told NBC News the U.S. is aware of the report and is monitoring the situation while "consulting closely with our Japanese and South Korean allies."
The report comes hours after Secretary of Defense Mark Esper met with South Korean President Moon Jae-in in Seoul.
On Friday, Trump told reporters that he received a "very beautiful letter" from North Korean leader Kim Jong Un. Trump also said he could have another meeting with Kim, but did not say when that meeting would take place.
Earlier this week, Pyongyang launched tactical guided missiles, which Kim said were a warning to the U.S. and South Korea, which had been conducting joint military drills. North Korea has conducted multiple weapons tests since June, when Kim and Trump had agreed to revive denuclearization talks.
The two leaders first met last year in a historic summit in Singapore. That was followed by a second round of talks in Vietnam in February, but that summit was abruptly ended after Trump reportedly handed Kim a note demanding he turn over Pyongyang's nuclear weapons and bomb fuel.
North Korea, the only nation to have tested nuclear weapons this century, spent most of Trump's first year in office perfecting its nuclear arsenal. While North Korea has paused nuclear tests that prompted Trump's threat to bring "fire and fury" upon that country, it had already made significant progress before the historic dialogue with the U.S. started.
Under the third-generation North Korean leader, the reclusive state has conducted its most powerful nuclear test, launched its first-ever intercontinental ballistic missile and threatened to send missiles into the waters near the U.S. territory of Guam.
— Reuters and NBC News contributed to this report.