Tensions have risen after North Korea conducted two missile tests in July which, like its five atomic bomb tests, were carried out in defiance of worldwide pressure and United Nations resolutions.
It described North Korea as the "strongest possessor" of intercontinental ballistic missiles capable of striking the U.S. mainland from anywhere.
US Pacific Command chief Admiral Harry Harris arrived in the South on Sunday to inspect the exercises and discuss growing North Korean nuclear and missile threats.
Two dozen Australian defence personnel are taking part in 10 days of war games between the USA and South Korea.
Speaking in Beijing, Chinese Foreign Ministry spokeswoman Hua Chunying said North and South Korea and the United States all needed to make more effort to ease tension.
The prime minister told 3AW last week that "if there is an attack on the U.S., the Anzus treaty would be invoked" and Australia would come to the aid of the United States.
The resolution imposes the toughest sanctions yet on North Korea including banning all exports of coal, iron, lead, and fish and seafood products valued at $1 billion " about a third of the country's total exports.
"In the event of a missile launch towards the territory of Japan, Guam, United States, Korea, we would take immediate, specific actions to take it down", Mattis said.
Both sides have since dialed back the rhetoric somewhat.
Guterres' remarks were not included but the United Nations chief told reporters Wednesday that he had spoken to the North Koreans and the five other parties in talks on Pyongyang's nuclear program that have been stalled since 2009.
The Japanese Defense Ministry wants to introduce a land-based Aegis missile defense system to address North Korea's missile threats and has chose to seek funding in the next fiscal year to cover the system design costs, a Japanese defense official told Reuters.
North Korea views such exercises as preparations for invasion and has fired missiles and taken other actions to show its anger over military drills in the past.
North Korean missiles would have to fly over Japan to reach the Guam area, worrying Tokyo that warheads or missile debris could fall on its territory.
The Pentagon says the USA and South Korea will begin a 10-day-long annual military exercise from Monday.
The drills involving tens of thousands of USA and South Korean troops are due to begin on Monday.
Pyongyang's state media yesterday called this year's drills a "reckless" move that could trigger the "uncontrollable phase of a nuclear war". This year, 17,500 members of the USA military and almost 50,000 servicemembers from the South Korean military are taking part. Much of it involves computer-based simulations.
"We will cooperate to advance trilateral and multilateral security and defence cooperation with other partners in the region, notably the Republic of Korea, Australia, India and other southeast Asian countries", Tillerson told reporters at a joint news conference with Kono, Mattis and Onodera.
Fan Changlong, a vice chairman of China's powerful Central Military Commission, told Dunford that China believed the only effective way to resolve the issue was through talks.
It is becoming increasingly clear an all-out war could erupt on the peninsula.
His comments about averting war echoed similar statements he made Tuesday that only South Korea could give consent to initiate any conflict with the North.