South Korea said it scrambled warplanes in response to 180 North Korean military flights near the countries' shared border on Friday, and Pyongyang again demanded that the United States and South Korea halt "provocative" air exercises.
The North Korean manoeuvres follow the firing of more than 80 rounds of artillery overnight and the launch of multiple missiles into the sea on Thursday, including a possible failed intercontinental ballistic missile (ICBM).
The United States called for a public U.N. Security Council meeting on Friday at which it accused Russia and China of providing "blanket protection" to North Korea from further U.N. Security Council action and said the pair had "bent over backwards" to justify Pyongyang's ballistic missile launches.
Representatives of both China and Russia in turn accused the United States of inflaming tensions with its large-scale joint military exercises with South Korea.
China's U.N. Ambassador Zhang Jun said that instead of playing up tensions, the United States should create conditions for the resumption of meaningful dialogue with North Korea.
In a joint statement after the meeting, the elected 10 members of the Security Council, who don't include China or Russia, which have permanent seats, condemned North Korea’s missile launches and called on the body to "speak with a unified voice on this matter."
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 Joint Chiefs of Staff said.
They flights occurred between 11 a.m. (0200 GMT) and 3 p.m. The virtual line is drawn north of the military border and is used as a basis for South Korean air defence operations, a South Korean official said.
He declined to give the virtual line's distance from the Military Demarcation Line (MDL) but local news reports said it was 20 to 50 km (12 to 31 miles).
South Korea scrambled 80 aircraft, including F-35A stealth fighters, in response, while about 240 jets participating in the Vigilant Storm air exercises with the United States continued their drills, the military said.
North Korea fired at least 23 missiles on Wednesday - a record for a single day.
The series of launches this week prompted the United States and South Korea to extend the Vigilant Storm military drills, which have angered Pyongyang.
North Korea's foreign ministry issued a statement saying the United States should stop its "provocative" air drills and warned that "sustained provocation is bound to be followed by sustained counteraction."
The Pentagon on Friday said the drills with South Korea were currently only being extended till November 5.
"We remain in close coordination with our ROK ally on any additional changes and the security environment on the Korean Peninsula," a U.S. military spokesman told Reuters.
Earlier, Pak Jong Chon, secretary of the Central Committee of North Korea's ruling Workers' Party, said Washington and Seoul had made a very dangerous decision by extending the exercises, and were "shoving" the situation out of control.
The high tensions on the Korean Peninsula come amid concerns that North Korea may be about to resume nuclear bomb testing for the first time since 2017.
A senior U.S. administration official said on Thursday that although the United States had said since May that North Korea was preparing to resume nuclear testing, it was not clear when it might conduct such a test.
The United States believes China and Russia have leverage to persuade North Korea not to resume nuclear bomb testing, the official told Reuters.
In recent years the U.N. Security Council has been split on how to deal with North Korea and in May, China and Russia vetoed a U.S.-led push to impose more U.N. sanctions in response to North Korean missile launches.
The North Korean foreign ministry statement referred to the U.N. meeting and said North Korea had been conducting "legitimate self-defensive" countermeasures.
A flight of 10 North Korean warplanes made similar manoeuvres last month, prompting South Korea to scramble jets.
In a joint statement on Friday, foreign ministers of the Group of Seven countries said any nuclear test or other reckless action by North Korea must be met with a swift, united, and robust international response.
Meeting in Washington on Thursday, U.S. Defense Secretary Lloyd Austin and South Korean Defense Minister Lee Jong-sup pledged to seek new measures to demonstrate the alliance's "determination and capabilities" following repeated North Korean provocations.
(Reporting by Josh Smith in Seoul; Additional reporting by David Brunnstrom and Chris Gallagher in Washington; Editing by Jack Kim, Gerry Doyle and Alistair Bell)
