New Delhi: South Korea on Thursday said North Korea has flown warplanes near the rivals' border, prompting it to scramble fighter jets, news agency AP reported. According to the report, South Korea's Joint Chiefs of Staff in a statement said that the North Korean warplanes flew as close as 12 kilometres north of the inter-Korean border between late Thursday and early Friday.


The South Korean Joint Chiefs of Staff said that it responded to the threat by scrambling F-35 jets and other warplanes. However, there were no reports of clashes between the rivals.


Notably, it is a highly unusual incident and it comes in the wake of tensions between the rivals that escalated over North Korea’s barrage of missile tests in the recent days.


Meanwhile, North Korea fired an unidentified ballistic missile into the sea off its east coast, South Korea's military said. This comes after the military said South Korea scrambled fighter jets, news agency Reuters reported.


According to the report, a subsequent statement on North Korea's official KCNA news agency quoted the North Korean military as saying that it took "strong military countermeasures" after South Korean artillery fire.


South Korea's Joint Chiefs of Staff statement said South Korean air force "conducted an emergency sortie with its superior air force, including the F-35A, and maintained a response posture, while carrying out a proportional response manoeuvre corresponding to the flight of a North Korean military aircraft."


Earlier in the day, North Korea test-fired a pair of long-range strategic cruise missiles, with leader Kim Jong Un hailing another successful display of the country's tactical nuclear strike capability, news agency AFP reported.


The North Korean leader expressed "great satisfaction" with the tests designed to boost the combat efficiency of the missiles "deployed at the units of the Korean People's Army for the operation of tactical nukes," KCNA said.


Kim "highly appreciated the high reaction capabilities of the nuclear combat forces," KCNA said.