The United States and South Korea have signed a new strategic pact that provides a "tailored" deterrence against North Korea's possible use of nuclear arms and other weapons of mass destruction amid growing threats from Pyongyang.
Of particular concern are North Korea's nuclear and ballistic missile programmes, its proliferation activities, and its chemical weapons
South Korean defence ministers agreed on Wednesday to review the timing and transfer of wartime command control of their combined forces on the Korean peninsula from US military to South Korea, a joint statement said.
While South Korea is scheduled to take over wartime operational command in 2015, there have been calls in the government for it to be postponed while North Korea continues to push ahead with its nuclear weapons and long-range missile programmes.
US Defence Secretary Chuck Hagel listened "very seriously" to their apprehensions.
"Of particular concern are North Korea's nuclear and ballistic missile programmes, its proliferation activities, and its chemical weapons," he said at a joint news conference with counterpart South Korea Defence Minister Kim Kwan-jin.
According to South Korean defence officials, North Korea has up to 5,000 tonnes of chemical weapons.
"Given these concerns, as Minister Kim noted, today we signed a bilateral strategy for tailored deterrence against the threat of North Korean nuclear weapons of mass destruction," Hagel said.
"There should be no doubt that North Korean use of chemical weapons would be completely unacceptable," he added.
North Korea conducted its third nuclear test in February, two months after launching a long-range rocket that put an object into space.