Photo/Illutration A TV screen at the Seoul Railway Station in South Korea shows a news program about North Korea's missile launch on Nov. 3 (AP Photo)

SEOUL—North Korea intensified its weapons action on Nov. 3 after the apparent failure of an intercontinental ballistic missile launched toward Japan and the announcement of an extension of a U.S.-South Korea military exercise.

Pyongyang fired six ballistic missiles on Nov. 3, followed by about 80 artillery rounds, according to South Korea’s Joint Chiefs of Staff.

The South Korean military immediately issued a warning to Pyongyang about the artillery fired close to its border.

“Such provocations upset the peace and stability of the Korean Peninsula and international community and must be stopped at once,” the military said.

The launch of the ICBM at around 7:40 a.m. likely ended in failure, according to the South Korean military, because the missile lost speed after the detachment of the second stage of the rocket.

Defense sources said the ICBM was likely a new type Hwasong-17 missile. Reaching a speed of Mach 15, the missile flew for about 760 kilometers and reached an altitude of about 1,920 km.

Japan’s Defense Ministry initially believed the missile would fly over Japanese territory, but that assessment was later revised after the missile disappeared from the radar screen.

Two short-range ballistic missiles were also launched on the morning of Nov. 3 while three missiles were fired later in the evening.

All six missiles landed in the Sea of Japan, outside of Japan’s exclusive economic zone.

After the missile launches, the U.S. and South Korean militaries announced they would extend the joint air force exercise that was initially scheduled to end on Nov. 4.

Since late September, North Korea has launched a large number of missiles to counter U.S. military maneuvers in the region.

Although many were short-range missiles, a North Korean ICBM flew over Aomori Prefecture in northern Japan on Oct. 4.

On Nov. 2, North Korea fired more than 20 missiles, including one that landed near the maritime border with South Korea.

(This article was compiled from reports by Kiyohide Inada and Takuya Suzuki.)