US Defence Secretary Ashton Carter and South Korean Defence Minister Han Min-koo warned North Korea of no tolerance for military provocations on Monday after the annual security meeting in Seoul.
"The minister and the secretary reaffirmed that any North Korean aggression or military provocation is not to be tolerated," they said in a joint statement.
"Both are stark reminders that North Korea is an up-close, dangerous and continuing threat to the security of the peninsula and the region," Carter said in the press conference, referring to the heavily armed border between the two Koreas and a 2010 attack against a South Korean navy ship Cheonan which the North rejected to have any role in the sinking.
Han said they “agreed that the alliance needs to work in various ways to cooperate and to rise against and respond” against the nuclear and missile threats from North Korea.
Carter also said their alliance "has never been stronger."
North Korea has vowed to continue its nuclear tests and launch a rocket to put a satellite into orbit, which is rejected by the US and South Korea as a long-range missile test.
The meeting came two months after the two Koreas traded artillery fire across their Demilitarised Zone between the two countries.
The two chiefs didn’t announce new steps on the wartime control of the South Korean Army, which they had decided last year to be based on conditions with no particular timeline.
The conditions include South Korean missile defenses and intelligence, surveillance and reconnaissance, ability to counter the North's artillery and rocket forces.
The US has the wartime control of the Seoul Army, besides its own troops in South Korea, since the 1950-53 Korean War.
The South gained peacetime control in 1994, and the two countries had lastly agreed the wartime control would be given by 2015, after the sides delayed a few times.
Han said "If we look at global trends in terms of national security, many countries in the world conduct self-defence in the form of cooperation with regional and local partners," when asked why South Korea was still not ready to take control of its own military.
The defence chiefs also agreed on cooperation in space and cyberspace, the joint statement said.
South Korea blames North for various cyber attacks in a wide range from banks and military institutions to media websites and TV broadcasts in recent years.
Carter, whose South Korea visit was first in his eight day Asia Pacific trip, then flies to Kuala Lumpur for Southeast Asian defence ministers meeting, which China is also expected to attend.
Commander of US Pacific Command, Admiral Harry Harris, who was in Seoul too, will fly to Beijing for his first visit to China in his duty.
US wants to advance its relationships and security cooperations with countries in the region and called its foreign policy, “rebalance,” a priority for its 21st century security interests.