North Korea has threatened "indiscriminate" nuclear strikes on the US and South Korea as the two begin their largest ever military drills.

The exercises, Key Resolve and Foal Eagle, are an annual event and always generate tension.

The order for a "pre-emptive nuclear strike of justice" was made in a statement put out by Pyongyang.

Such rhetoric is not uncommon, and experts doubt the North's ability to put nuclear warheads on its missiles.

North Korea says it sees the annual US-South Korean war games as a rehearsal for invasion. Last year, it threatened to turn Washington into a "sea of fire".

"We will launch an all-out offensive to decisively counter the US and its followers' hysteric[al} nuclear war moves," a newsreader on the state-run North Korean KRT news channel said of the latest exercises.

Approximately 17,000 US forces are participating in the exercises, alongside around 300,000 South Korean troops - both significant increases on 2015's numbers.

Despite starting on the same day, Key Resolve is more computer simulation-driven and ends on 18 March, while Foal Eagle is more focussed on field exercises and runs until 30 April.

The South's defence ministry has warned Pyongyang against any "rash act that brings destruction upon itself".

"If North Korea ignores our warning and makes provocations, our military will firmly and mercilessly respond to it," said spokesman Moon Sang-gyun.

Japan's foreign minister also demanded that North Korea show restraint.

"North Korea's nuclear, and nuclear missile development is absolutely unacceptable. We will coordinate with the international community to demand that North Korea show restraint, and abide by the various resolutions including that of the six party talks," said Fumio Kishida.

Though unconfirmed, South Korea's Yonhap news agency, citing military sources, has reported that the exercises will include training for precision attacks on North Korean leadership and its nuclear and missile facilities.

(BBC)