North Korea fired an unidentified projectile eastward Friday, South Korea's military said, hours after it warned of a "stronger and certain" response following the United States' imposition of new sanctions.

The Joint Chiefs of Staff (JCS) announced the launch, the third in a little over a week, without elaborating further.

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 US 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. (Yonhap)