South Korea has raised its military alert amid “imminent signs” that North Korea may be preparing for a missile launch.

South Korean intelligence says the North has finished preparations to launch one or two Musudan medium-range missiles from its east coast, prompting Seoul to turn its military watch alert up a notch to “vital threat” on Wednesday.

Yonhap quoted a government source as saying Pyongyang might be preparing “multiple” launches, after other launch vehicles were reportedly detected carrying shorter-range SCUD and Rodong missiles.

“They could fire the Musudan, Scud and Rodong missiles simultaneously or launch one of them” the defence ministry said. “We’ve stepped up monitoring in case of any missile launches.”

Speculation of a missile launch has mounted ahead of the anniversary of the birth of North Korea’s founder, Kim Il-sung, on April 15 – a timely occasion for the North to showcase its military might following a torrent of warlike rhetoric.

North Korea warned foreigners in South Korea to evacuate ahead of a “thermonuclear war” on the peninsula. Diplomatic missions were also told to withdraw from Pyongyang because it could no longer guarantee their safety “when” war erupts.

The US said it was confident it could detect and intercept North Korean missiles but went against shooting it down unless its allies are at risk.