South Korea and the United States have signed a new military plan that lays out how the allies will communicate with each other and react to any future North Korean aggression.
The signing of the pact on Monday comes amid North Korean threats to attack the allies over their joint military drills and recent punishing UN sanctions aimed at Pyongyang's latest nuclear test.
Seoul's joint chiefs of staff said the plan is designed to counter a future limited attack by North Korea.
While existing agreements provide for US engagement in the event of a full-scale conflict, the new protocol addresses the response to low-level action such as a limited cross-border incursion.
It guarantees US support for any South Korean retaliation and allows Seoul to request any additional US military force it deems necessary.
"This allows both nations to jointly respond to the North's local provocations, with the South taking the lead and the US in support," Kim Min-Seok, South Korea’s defence ministry spokesman, said.
"It will have the effect of preventing the North from daring to provoke us," Kim told reporters.
The "provocative" scenarios envisaged by the new pact include maritime border incursions, shelling of border islands, and infiltration by low-flying fighter jets or special forces.
General Jung Seung-Jo, the chairman of the South's Joint Chiefs of Staff, said the accord would allow for "strong retaliation" that would make North Korea "bitterly regret" any provocative move.
Wave of threats
The US has close to 30,000 troops stationed in South Korea with the option to bring in reinforcements from its military bases in Japan.
The protocol was signed just days before the third anniversary of the 2010 sinking of a South Korean warship, the Cheonan, which left 46 dead.
South Korea said it was sunk by a North Korean torpedo, although Pyongyang had always denied any involvement.
Later the same year, North Korea shelled the South Korean border island of Yeonpyeong, killing four people.
Angered by UN sanctions imposed after its nuclear test in February, North Korea has issued a wave of threats over the past month - ranging from a surgical military strike to nuclear war.
The North's young leader Kim Jong-Un recently made a series of visits to frontline military units across the country, during which he threatened South Korean military units.
During a trip on Monday to Baengnyeong marking the 2010 sinking, South Korean Defence Minister Kim Kwan-Jin accused the North's leader of heightening military tensions.
Meanwhile, South Korea on Monday held a naval exercise involving combat corvettes and missile patrol ships close to the disputed maritime border.
The de-facto maritime boundary - the Northern Limit Line - is not recognised by Pyongyang, which argues it was unilaterally drawn by the US-led United Nations forces after the 1950-53 Korean War.
It was the scene of deadly naval clashes in 1999, 2002 and 2009.
On Tuesday, newly elected President Park Geun-Hye and top military officials will attend a memorial ceremony at the national cemetery in Daejeon, where the victims of the Cheonan sinking are buried.