SEOUL - South Korea said it scrambled warplanes in response to 180 North Korean military flights near the countries' shared border on Friday, hours after the North fired about 80 artillery rounds in protest of Seoul's joint military drills with the United States.

North Korean aircraft were detected in multiple areas north of the "tactical action line" north of the Military Demarcation Line between the two Koreas, according to South Korea's Joint Chiefs of Staff.

The 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 MDL, but local news reports said it was 20 to 50 kilometres (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.

A flight of 10 North Korean warplanes made similar manoeuvres last month, prompting South Korea to scramble jets.

The North's 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).

North Korea also fired at least 23 missiles on Wednesday - a record for a single day.

The series of launches prompted the United States and South Korea to extend the Vigilant Storm drills, which have angered Pyongyang.

Meeting in Washington, 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, according to a joint statement between the two countries.

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 for the first time since 2017, 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.

Diplomats said Washington had asked the U.N. Security Council to convene publicly on North Korea on Friday, a request backed by other council members Britain, France, Albania, Ireland and Norway.

In recent years the 15-member 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.

In Seoul, German President Frank-Walter Steinmeier condemned North Korea for threatening international security with repeated missile launches and urged Pyongyang to return to dialogue.

"I think the Pyongyang regime is solely responsible for the current situation," Steinmeier said via an interpreter during a news conference after talks with South Korean President Yoon Suk-yeol.

Pyongyang, meanwhile, has condemned allied military drills.

On Thursday, 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 United States and South Korea will find that they have made a terrible mistake that cannot be reversed," said Pak.

(Reporting by Josh Smith; Editing by Jack Kim and Gerry Doyle)