SEOUL — The US military said Monday it had signed an agreement 2½ years in the making to support South Korea in countering North Korean provocations.
The mutual defense treaty with South Korea obligates the US military to fight to defend its ally if a war breaks out on the Korean Peninsula.
The deal, signed Friday, defines what role the United States would play in dealing with what South Korean military officials called ‘‘local’’ provocations from the North, such as its shelling of a border island in 2010, which killed four South Koreans. The two allies said they had been working to improve their contingency plans since that attack.
They called the contingency plan ‘‘South Korean-led, US-supported.’’ It laid out various types of localized North Korean provocations and a joint South Korean-US response to each of them, South Korean officials said.
By putting the allies’ combined commitment on paper, the agreement will help serve as a deterrent against North Korean provocations, they said.
But the two allies refused to disclose more details on such potentially volatile questions as how far the United States would go in its supporting role, especially at what point US troops would directly join a counterattack against a North Korean provocation.
In recent weeks, South Korea has said that if provoked, it would attack not only the origin of the North Korean provocation but also ‘‘its supporting forces and its commanding post.’’
“By completing this plan, we improved our combined readiness posture to allow us to immediately and decisively respond to any North Korean provocation,’’ a joint statement from the two allies said.
The plan was signed by General James D. Thurman, the top US commander in South Korea, and General Jung Seung-jo, chairman of the Joint Chiefs of Staff of the South Korean military.