SEOUL, South Korea — North Korea on Monday threatened to launch nuclear strikes at the United States and its military bases in Northeast Asia as the United States and South Korea began one of their annual large-scale joint military exercises.

Thousands of American Marines and other troops arrived in South Korea in the past week for the exercises, which will involve 17,000 American and 300,000 South Korean troops. The drills test the allies’ ability to respond to North Korean attacks on the Korean Peninsula.

North Korea has made similar threats before, characterizing the exercises as rehearsals for an invasion. But this year, tensions are raised even higher because of the North’s recent nuclear test and the ensuing international condemnations.

Last month, after the North launched a long-range rocket to put a satellite into orbit, the South Korean Defense Ministry announced that this year’s drills would be the largest ever. The nuclear-powered aircraft carrier John C. Stennis will join the exercises, the American and South Korean militaries said in a joint statement on Monday.