In this photo provided by South Korea Defense Ministry, U.S. Air Force F-35B stealth fighter jets drop bombs as they fly over the Korean Peninsula during a joint drills, South Korea on Monday, Sept. 18, 2017.
The Philippines on Saturday repeated its call on North Korea to stop its "provocations" and instead engage in talks to ease tensions after the rogue state conducted another missile launch in the face of tougher global sanctions. Sanctions are not "a tool for stifling the regime", it said.
The US said it conducted the new military exercise with the South in response to the North's recent missile and nuclear tests, said the source.
Pyongyang carried out the latest in a rapid series of missile launches by firing another mid-range ballistic missile over Japan on Friday, soon after its sixth and most powerful nuclear test on September 3, in defiance of United Nations sanctions and other worldwide pressure.
Seoul is within artillery range of North Korea, which is also believed to have a sizeable chemical and biological arsenal beyond nuclear and conventional weapons.
They were 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.
"America and our allies will never be intimidated", Trump said in a wide-ranging speech Friday marking the 70th anniversary of the Air Force at Joint Base Andrews, Md."We will defend our people, our nations and our civilization from all who dare to threaten our way of life". Mattis confirmed that policy on Monday, saying it would not shoot down a North Korean missile unless it poses a direct threat to the United States or its allies.
Recently, the USA and its vassal forces rigged up the UNSC "resolution 2375" on sanctions harsher than ever against the DPRK branding its measures to strengthen the state nuclear force as "a threat" to global peace and security, and released a UNSC "press statement" calling for the implementation of the "resolution" as a follow-up.
Monday's flyovers came three days after North Korea fired an intermediate-range missile over Japan into the northern Pacific Ocean in apparent defiance of USA -led worldwide pressure on the country.
Asked whether there were any military options the United States could take with North Korea that would not put Seoul at grave risk, Mattis said: "Yes there are".
The relocation came after a North Korean missile was test-fired last week and flew over southern Hokkaido and landed in the Pacific off the island's east coast - the second flyover in less than a month.