South Korea and the US have announced that their annual military drills will take place from 24 February to 18 April, despite anger from North Korea.
Pyongyang warned against the planned drills last week, calling them "exercises of war".
Meanwhile, the US said it was disappointed that the North rescinded an invitation to a US envoy to discuss the release of a jailed US citizen.
Kenneth Bae has been held in North Korea for more than a year.
In a statement on Monday, the joint Combined Forces Command (CFC) said that Key Resolve, a computer-based simulation, and Foal Eagle, which involves air, ground and naval drills, were both scheduled to begin on 24 February.
"Key Resolve is a vital exercise to strengthen readiness of the Republic of Korea and US Alliance," CFC commander Gen Curtis Scaparrotti said.
"The scenarios are realistic, enabling us to train on our essential tasks and respond to any crisis which may arise."
Last year, the exercises led to a prolonged surge in tensions, with North Korea threatening pre-emptive nuclear strikes and cutting a military hotline with the South.
North Korea's top military body threatened last week to cancel planned family reunions with the South if the joint military exercises went ahead.
The reunions are for family members separated when the Korean peninsula was partitioned at the end of the 1950-53 Korean War. However, the North has been accused of using them as a bargaining chip.
South Korean defence ministry spokesman Kim Min-seok said on Monday: "North Korea is well aware that the South Korean-US drills are annual trainings defensive in nature."
"So it is not appropriate to link [the drills] with family reunions."