The US flew four stealth fighter jets and two bombers over the Korean peninsula on Monday in a show of force after North Korea's latest nuclear and missile tests.
A pair of US B-1B bombers and four F-35 jets flew from Guam and Japan, and joined four South Korean F-15K fighters in the latest drill, South Korea's defence ministry said.
The joint drills were being conducted "two to three times a month these days", Defence Minister Song Young-moo told a parliamentary hearing on Monday.
They would be the first flights since the North conducted its sixth and most powerful nuclear test on September 3 and staged an intermediate-range missile test over Japan last Friday, sending regional tensions soaring.
The previous such flights were on August 31. The US military could not immediately confirm the latest flights.
The US is ramping up pressure on the North, with its ambassador to the UN Nikki Haley warning that Pyongyang would be "destroyed" if it refused to end its "reckless" weapons drive.
Efforts to tame the increasingly belligerent North are set to dominate US President Donald Trump's address to the UN General Assembly and his meetings with South Korean and Japanese leaders this week.
Tensions flared again when Kim Jong-Un's regime tested what it termed a hydrogen bomb many times more powerful than its previous device.
The North also fired a ballistic missile over Japan and into the Pacific on Friday, responding to new UN sanctions over its atomic test with what appeared to be its longest-ever missile flight.
Mr Trump and South Korean President Moon Jae-In spoke by phone Saturday and vowed to exert "stronger pressure" on the North, with Mr Moon's office warning further provocation would put it on a "path of collapse".
The US president has also not ruled out a military option, which could leave millions of people in the South Korean capital - and 28,500 US soldiers stationed in the South - vulnerable to potential retaliatory attack.
Trump's National Security Advisor H.R. McMaster said the US would "have to prepare all options" if sanctions prove insufficient to stop the North's weapons drive.
China, US start naval drills after latest missile launch
Meanwhile China and Russia have begun naval drills near North Korea amid continuing tensions over the isolated state's nuclear ambitions.
The official Xinhua news agency said the joint exercises will take place between Peter the Great Bay, just outside of the Russian far eastern port of Vladivostok, not far from the Russia-North Korea border, and into the southern part of the Sea of Okhotsk, to the north of Japan.
The drills are the second part of China-Russian naval exercises this year, the first part of which took place in the Baltic in July. The report did not directly link the drills to current tensions over North Korea.
A week ago, the 15-member UN Security Council unanimously adopted its ninth sanctions resolution since 2006 over North Korea's nuclear and ballistic missile programs.
North Korean diplomats will have a front-row seat in the UN General Assembly for Trump's speech on Tuesday morning, which will touch on the escalating crisis that has seen Trump and Pyongyang trade threats of military action.
Ms Haley said on Sunday the UN Security Council has run out of options on containing North Korea's nuclear program and the United States may have to turn the matter over to the Pentagon.
