SEOUL - North Korea Saturday fired what appeared to be two short-range ballistic missiles into the sea after vowing to remain the biggest "threat" to the United States and branding Secretary of State Mike Pompeo as "toxin."

It was the latest in a series of short-range missile tests the nuclear-armed nation has carried out in recent weeks in protest against US-South Korean military exercises, which it sees as a rehearsal for invasion. The latest joint drill wrapped up on Tuesday.

"The military detected two unidentified projectiles presumed to be short-range ballistic missiles," South Korea's Joint Chiefs of Staff in a statement Saturday after the latest launch.

The missiles flew about 380 kilometers and reached an altitude of 97 kilometers at a top speed of Mach 6.5 before landing in the East Sea, also known as Sea of Japan, it said.

"Our military is tracking the movement in the North in case of additional launches, with firm readiness," it added.

South Korea's presidential Blue House convened a National Security Council meeting and expressed "grave concerns" in a statement, pointing out Pyongyang had carried out the launch after the joint US-South Korea military drills had ended.

"NSC members agreed to continue diplomatic efforts with the international community to bring the North back to negotiation table with the US to achieve the goal of complete denuclearization in the Korean peninsula."

Tokyo also believed North Korea had fired "ballistic missiles" in violation of UN resolutions, Japanese Defense Minister Takeshi Iwaya told reporters.

"It can't be overlooked no matter what the size and distance are," he said.

Washington was monitoring the situation following reports of a missile launch, a senior US official said.

"We are consulting closely with our Japanese and South Korean allies." -AFP