A TV screen shows file images of North Korea's missile launch during a news program at the Seoul Railway Station in Seoul, South Korea, Thursday, Oct. 13. AP-Yonhap

North Korea on Friday fired a short-range ballistic missile (SRBM) into the East Sea and about 170 artillery shots into maritime "buffer zones" set under a 2018 inter-Korean military tension reduction accord, the South Korean military said.

The provocative move came after more than 10 North Korean warplanes staged menacing flights close to the inter-Korean border, prompting the South Korean Air Force to scramble its F-35A stealth fighters and other assets to the scene, according to the Joint Chiefs of Staff (JCS).

The JCS said it detected the SRBM launch from the Sunan area in Pyongyang at 1:49 a.m., and that the missile flew some 700 kilometers at an apogee of 50 km at a top speed of about Mach 6.

It also detected the North's firing of some 130 artillery shots into the Yellow Sea from Majang-dong, Hwanghae Province, between 1:20 a.m. and 1:25 a.m., and of some 40 artillery shots into the East Sea from Gueup-ri, Gangwon Province, between 2:57 a.m. and 3:07 a.m.

The artillery shots landed in eastern and western buffer zones north of the Northern Limit Line, the de facto inter-Korean sea border, which were delineated under the two Koreas' Comprehensive Military Agreement (CMA) signed on Sept. 19, 2018, to reduce tensions.

The North's Korean People's Army said later via the country's state media that it took "strong countermeasures" in response to what it claims to be a 10-hour-long South Korean artillery exercise.

Seoul officials said the artillery exercise in question was conducted by the U.S. Forces Korea at a firing range in Cheorwon, some 71 km northeast of Seoul, from 8 a.m. through 6 p.m. on Thursday, involving multiple launch rocket systems (MLRS).

The JCS issued a statement criticizing the artillery firing and the SRBM launch as a "clear" violation of the CMA and U.N. Security Council resolutions, respectively.

"Our military gravely warns North Korea regarding the fact that it has violated the Sept. 19 military agreement and escalated military tensions on the Korean Peninsula through continued provocations, and strongly urges it to immediately cease them," the JCS said.

It added, "Our military will keep maintaining a firm readiness posture based on capabilities to respond overwhelmingly to any North Korean provocations."