SEOUL, Mar. 5 (Reuters) - North Korea's defence ministry urged South Korea and the United States to stop military drills, saying they are rehearsals of war and warning of consequences, KCNA reported on Tuesday.

South Korean and U.S. militaries kicked off their annual spring exercises on Monday with twice the number of troops joining compared to last year, seeking to improve their responses to North Korea's evolving nuclear and missile threats.

An unnamed spokesperson of Pyongyang's defence ministry said it strongly denounces what it called "frantic, reckless" military drills, urging them to stop, KCNA said.

The exercises can never be defensive but are an attempt to invade the North, the spokesperson said, pointing to their increased scale and the participation of 11 member countries of the United Nations Command.

"A nuclear war may be ignited even with a spark," KCNA quoted the spokesperson as saying.

The United States and South Korea will have to "pay a dear price for their false choice," the official added, vowing to conduct "military activities to strongly control the unstable security environment."

The Freedom Shield exercises, set to end on March 14, came as North Korea pushes to develop its nuclear capabilities with missile and other weapons tests.

The exercises are primarily designed to neutralise the North's nuclear threats, including by "identifying and striking" cruise missiles, which Pyongyang had indicated could carry nuclear warheads, Seoul military officials said.

Pyongyang has angrily reacted to the allies' military drills, calling them rehearsals for a nuclear war.

Seoul and Washington say the exercises are defensive and a response to the North's threats.

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