An American military base in South Korea accidentally blared an alert siren instead of a bugle call, causing a brief scare just as the United States and its allies are monitoring for signs of provocation from North Korea, which has warned it could send a “Christmas gift” over deadlocked nuclear negotiations.

The siren at Camp Casey, which is near the border with North Korea, went off by “human error” at approximately 10pm local time on Thursday, Lt Col Martyn Crighton, a public affairs officer for the second Infantry Division said on Saturday.

The operator immediately identified the mistake and alerted all units at the base of the false alarm, which did not interfere with any operations, Crighton said in an email.

The incident came a day before Japanese broadcaster NHK caused panic by mistakenly sending a news alert saying North Korea fired a missile over Japan that landed in the sea off the country’s northeast island of Hokkaido early on Friday.

The broadcaster apologised, saying the alert was for media training purposes.

North Korea has been dialling up the pressure on Washington ahead of an end-of-year deadline issued by leader Kim Jong Un for the Trump administration to offer mutually acceptable terms for a nuclear deal.

There are concerns that Pyongyang could do something provocative if Washington does not back down and relieve sanctions imposed on the North’s broken economy.

The North fired two missiles over Japan during a provocative run in weapons tests in 2017, which also included three flight tests of developmental intercontinental ballistic missiles that demonstrated potential capabilities to reach the US mainland.

Tensions eased after Kim initiated diplomacy with Washington and Seoul in 2018 while looking to leverage his nukes for economic and security benefits.

But negotiations have faltered since a February summit between Kim and President Donald Trump broke down after the US side rejected North Korean demands for broad sanctions relief in exchange for a partial surrender of its nuclear capabilities.

In a statement issued earlier this month, North Korean senior diplomat Ri Thae Song asserted that the Trump administration was running out of time to salvage faltering nuclear negotiations, and said it is entirely up to the United States to choose what “Christmas gift” it gets from the North.

The North also in recent weeks said it conducted two “crucial” tests at a long-range rocket facility it said would strengthen its nuclear deterrent, prompting speculation that it is developing a new ICBM or preparing a satellite launch.