South Korean Marines get off from a helicopter during a military drill. File photo/AFP

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

North Korea threat looms as China, Japan, South Korea leaders meet

The siren at Camp Casey, which is near the border with North Korea, went off by "human error" at around 10pm on Thursday, said Lt. Col. Martyn Crighton, a public affairs officer for the 2nd Infantry Division.

A man watches a TV showing a file image of a North Korea's missile launch in Seoul, South Korea. File photo/AP

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 Saturday.

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 northeastern island of Hokkaido early on Friday. The broadcaster apologized, saying the alert was for media training purposes.

North Korea has been dialing up 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 doesn’t 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.

Associated Press