South Korea and the US have carried out wargames in the Sea of Japan, less than a week after two US nuclear-capable bombers flew over the Korean Peninsula for the second time this month.
The navies put on a show of force in waters east of the Korean Peninsula on Monday, with US guided missile destroyer USS Spruance joining other warships.
South Korea also deployed its submarines and planes to the sea as well as destroyers which are equipped with the Aegis missile defense system.
The US conducted a second flyover since September 9 over the Korean Peninsula on Wednesday. A pair of B-1B Lancer strategic bombers, escorted by US and South Korean fighter jets, crossed the demarcation line separating the two Koreas.
According to the US Air Force, it was the closest ever to the border with the North by a B-1 bomber.
North Korea condemned the flight as an armed provocation that mobilized "ill-famed nuclear killing tools."
The US has been increasing its military presence in the region, prompting North Korea to warn provocative moves were pushing the peninsula to “the point of explosion.”
Pyongyang conducted its fifth nuclear test on September 9. It announced this week that it had successfully tested a new rocket engine that would be used to launch satellites. It also tested a submarine-launched ballistic missile in August.
South Korean officials say the North is physically ready to conduct its sixth nuclear test.
In the wake of this month's nuclear test, the United Nations Security Council threatened to prepare a new round of sanctions against Pyongyang, which has already been under strict sanctions since 2006.
North Korea’s Foreign Minister Ri Yong Ho told the UN General Assembly on Friday that his country will strengthen its nuclear capabilities despite the threat of new sanctions.
He said the US and "its hostile policy" against Pyongyang has turned the Korean Peninsula “into the world's most dangerous hot spot which can even ignite the outbreak of a nuclear war."
The US, which has about 28,500 troops in South Korea, is planning to deploy its Terminal High-Altitude Area Defense (THAAD) system in the South by the end of next year.
North Korea has threatened to carry out “physical action” in response to the measure.