(ATTN: UPDATES with details in para 4)
By Song Sang-ho
SEOUL, Jan. 14 (Yonhap) -- North Korea fired two suspected ballistic missiles eastward Friday, South Korea's military said, after Pyongyang publicly warned earlier in the day of a "stronger and certain" response to the United States' imposition of new sanctions.
The Joint Chiefs of Staff (JCS) said the short-range projectiles were launched from Uiju in North Pyongan Province, a northwestern region bordering China, and that they flew around 430 kilometers at an altitude of 36 km.
It detected one of the missiles at 2:41 p.m and the other at 2:52 p.m.
The missiles flew at top speed of around Mach 6, six times the speed of sound, according to officials.
The intelligence authorities of South Korea and the United States are conducting a detailed analysis for more information, the JCS said.
"At this point, it seems that the North fired the missiles toward pre-set targets so as to verify the missiles' accuracy," a JCS official told reporters on condition of anonymity.
"It is presumed to be a set of test launches aimed at enhancing the accuracy of the existing short-range ballistic missiles," he added.
The targets in point are thought to have been set on Al Island, an uninhabited island off the North's east coast, sources said.
The North's latest saber-rattling marks its third show of force this year.
South Korea's military is monitoring related North Korean movements and maintaining a firm readiness posture, the JCS said.
Earlier in the day, Pyongyang issued the warning after Washington slapped the sanctions on six North Koreans involved in the regime's weapons of mass destruction and ballistic missile programs Wednesday.
"If the U.S. adopts such a confrontational stance, the DPRK will be forced to take stronger and certain reaction to it," a spokesperson of the foreign ministry said in a statement carried by the North's official Korean Central News Agency. DPRK stands for the North's official name, the Democratic People's Republic of Korea.
The North fired what it claims to be hypersonic missiles on Jan. 5 and Tuesday, in an apparent quest for new advanced weapons amid a deadlock in nuclear talks with the United States.
Meanwhile, the U.S. Indo-Pacific Command said that it is aware of the missile launches, but assessed they do "not pose an immediate threat to U.S. personnel or territory or to our allies."
"The missile launch highlights the destabilizing impact of the DPRK's illicit weapons program," it said in a press release. "The U.S. commitment to the defense of the Republic of Korea and Japan remains ironclad."