South Korea and the United States on Monday launched a major joint air exercise to deter North Korean provocations amid high cross-border tensions, officials said.
The annual drill called "Max Thunder" will run through May 18 and this year involves about 60 planes including jet fighters, KC-135 refuelling aircraft and AWACS surveillance planes, the South's air force said in a statement.
The allies will display their readiness and joint air firepower in war situations, it said, adding US and South Korean pilots would train for "precision strikes on the origin of provocations by the enemy".
"This year's drill is the biggest of its kind since Max Thunder began in 2008," an air force spokesman told AFP.
Pyongyang habitually fiercely denounces annual joint exercises by US and South Korean troops but has not physically responded to them. Seoul and Washington say they are merely defensive in nature.
The North has threatened "sacred war" against the South in retaliation for perceived insults during Pyongyang's commemoration in April of the centenary of the birth of founding leader Kim Il-Sung.
Last week the North's new leader Kim Jong-Un inspected an air force unit, the latest in a series of military visits since he took over after his father died last December.
South Korean and US officials have pledged a tough response to any provocations by the North. Some 28,500 US troops are based in the South.
The South accuses the North of torpedoing a warship near the disputed Yellow Sea border in March 2010 with the loss of 46 lives. The North denied the attack but shelled a South Korean border island in November that year, killing four.