South Korea and the United States have begun a new round of joint military exercises on Monday, officials say, the second round to take place this year.
Thousands of soldiers are taking part in computer-aided drills designed to test defense capabilities.
South Korea says that North Korea, which was angered by the previous drill, was notified well in advance.
The drills come as the North agreed to family reunions and reached a deal with the South on an industrial zone.
The drills, known as Ulchi Freedom Guardian, are expected to last for 12 days and mobilizes about 50,000 members of the South Korean military and 30,000 US servicemen, reports Yonhap news agency.
South Korea and the US have begun a new round of joint military exercises on Monday, the second to take place this year
They are intended to help “ensure stability and security on the peninsula and reaffirm the US commitment to the north-east Asia region”, says a statement from the United States Forces Korea.
The drills come as tensions are starting to ease in the peninsula.
On Sunday, North Korea agreed to a South Korean proposal to resume in September reuniting families separated since the 1950-1953 Korean War.
Many families were separated at the end of the war by the dividing of the peninsula. The two sides remain technically at war, because the conflict ended in an armistice and not a peace deal. The last reunions were held in 2010.
Last week, officials of the two Koreas also reached an agreement about re-opening the Kaesong joint industrial zone – the last functioning inter-Korean joint project and a key source of revenue for Pyongyang.
The Kaesong Industrial Complex, which lies just inside North Korea, is home to 123 South Korean factories which employ more than 50,000 North Korean workers.
North Korea withdrew its workers in April, angered by the expansion of UN sanctions after its February 12 nuclear test and annual US-South Korea military drills.
The accord came after six rounds of talks ended unsuccessfully.
The United States has decided to delay Minuteman III intercontinental ballistic missile (ICBM) test scheduled for next week, Pentagon officials have announced.
The Minuteman III ICBM test was put off over concerns it could be misinterpreted by North Korea, amid fears of a conflict.
The test could be postponed till May, in what correspondents say will be portrayed by Pyongyang as a victory.
North Korea has issued a series of unusually strong threats since it was sanctioned by the UN in March for carrying out a third nuclear test.
The Minuteman III ICBM test was put off over concerns it could be misinterpreted by North Korea, amid fears of a conflict
The communist country has threatened nuclear strikes on the US, formally declared war on South Korea, and pledged to reopen a nuclear reactor in defiance of UN Security Council resolutions.
A Pentagon official said the US wanted to “avoid any misperception or miscalculation” that might result from the Minuteman 3 test.
The US and South Korean officials have sought to play down fears of a conflict on the Korean peninsula in recent days.
Pyongyang will likely use the delay to its advantage in propaganda, and say the US has been forced to climb down in the face of resilience from the North Korean army.
The North Korean media are full of images of military preparedness intended to rally people behind the leadership.
On Friday, North Korea warned it would not be able to guarantee the safety of embassy staff in the event of a war, but no foreign governments have announced plans to evacuate their embassies.
Many of North Korea’s angry statements have cited annual military exercises between US and South Korean forces as provocation.
The US flew nuclear-capable B2 and B52 bombers over the South as part of the drill, and has since deployed warships with missile defense systems to the region.
This week, North Korea reportedly moved at least one missile to its east coast. It has threatened to strike the Pacific island of Guam, where the US has a military base.
North Korea’s missiles have the capability to carry nuclear warheads, but the country is not yet thought to have developed such warheads.
Many observers say that North Korea’s belligerent rhetoric appears intended for a domestic audience and at shoring up the position of Kim Jong-un, who came to power after his father’s death in December 2011.