The U.S. and South Korean defense chiefs urged North Korea on Monday to immediately cease all activities related to its nuclear program and said they will have no tolerance for any military provocation by Pyongyang.
U.S. Defense Secretary Ash Carter and South Korean Defense Minister Han Min-koo also expressed "grave concern" over the North's intent to conduct a long-range missile launch and a nuclear test, a joint statement issued after their talks said.
"Both are stark reminders that North Korea is an upclose, dangerous and continuing threat to the security of the peninsula and the region," Carter told a news conference with Han, referring to the heavily armed border between the two Koreas and a 2010 attack against a South Korean navy ship.
North Korea denies any role in the sinking of the Cheonan, which Seoul blames on Pyongyang.
"The minister and the secretary reaffirmed that any North Korean aggression or military provocation is not to be tolerated," the statement said.
North Korea has vowed to conduct nuclear tests and continue the launch of what it says is a rocket to put a satellite into orbit, a claim rejected by the United States and South Korea as a disguised long-range missile test.
Carter and Han met in Seoul on Monday in an annual review of their combined defense readiness against the North and to discuss operational command of their joint forces in case tensions with North Korea escalate into a war.
The meeting came two months after North and South Korea resolved a military standoff that had threatened to escalate into live conflict after exchanging artillery fire across their Demilitarized Zone (DMZ) border.
The two ministers also agreed to boost cooperation in space and cyberspace to improve the security of critical infrastructure, including information and space systems, the joint statement said.
They also agreed on a plan for the transfer of operation control of their combined troops in case of war as Seoul improves its readiness with better capabilities, it said. There were no details available about the plan.
The United States has around 28,500 troops in South Korea.
The United States and South Korea have agreed that South Korea would need to improve its intelligence, surveillance, and reconnaissance capabilities and its ability to defend itself from artillery attacks before it assumes control of their combined forces in wartime, Carter told the news conference.
Carter flies to Malaysia later for a meeting of Southeast Asian defense ministers, which China's Defense Minister Chang Wanquan is also due to attend.