North Korean aircraft were detected in multiple areas north of the "tactical action line" north of the Military Demarcation Line between the two Koreas.
South Korea's Yonhap news agency reported on Saturday North Korea may be preparing to test a submarine-launched ballistic missile (SLBM), citing the South's military.
The US Defense Department announced that hypersonic weapons and defense development are among its top priorities for the next year.
The US has. in the past, expressed concerns satellite launches could help Iran develop ballistic missiles.
"Sarmat" has the longest operational range in the world, according to Russia, which will significantly increase the combat power of the country's strategic nuclear forces.
Analysts say that more testing could help North Korea reach its stated goals of making smaller nuclear warheads and improving their reliability.
Tensions on the Korean peninsula have been rising amid growing signs that Pyongyang could soon follow through on its threats to restart testing ICBMs, breaking a self-imposed 2017 moratorium.
The report says North Korean leader Kim Jong Un remained strongly committed to expanding his nuclear weapons arsenal and ballistic missile research and development.
President elect Joe Biden is expected to attempt to rejoin the nuclear deal with Iran
Although it still remains unclear if the missile is ready for use or whether it is just in an advanced phase of field testing, its deployment by the ministry has led to concerns in the West.