North Korea earthquake prompts fears of 'new' nuclear test by Kim Jong-un

The tremor followed an exchange of military fire between the Koreas the day before

The planned North Korean drills come after an increase in threatening rhetoric from Pyongyang and a series of rocket and ballistic missile launches in an apparent protest against the annual military exercises by Seoul and Washington

A magnitude 5.1 earthquake located off the west coast of South Korea has occurred just days after North Korea threatened to conduct a “new form” of nuclear test, the United States Geological Survey (USGS) has said.

The quake centered about 100 km north-west of the West Gyeongnyeolbi Archipelago, off Taean County, and was the third strongest in or around the Korean peninsula since official seismological records began in 1978.

On Sunday, North Korea warned it “would not rule out a new form of nuclear test for bolstering up our nuclear deterrence,” but did not give any further details on what this would entail, in response to United Nations Security Council's condemnation of the country’s recent ballistic missile launch.

The earthquake took place at a depth of nearly 16km (10 miles) in the sea west of the Korean peninsula, which did not immediately suggest North Korean nuclear testing was the cause, according to The Telegraph.

Meanwhile, an unmanned drone crashed on a South Korean island near a disputed maritime border with North Korea, a South Korean defence ministry official said on Tuesday, triggering an investigation into whether the aircraft was from the North.

The South Korean military was trying to verify where the drone had come from and what its purpose might have been, and was also looking into any possible link to North Korea's espionage operations, a military official told Reuters.

On Monday, North and South Korea fired artillery shells into each other's waters, forcing people on five South Korean islands on the frontline to evacuate their homes.

Early that morning, North Korea announced that it would conduct live-fire drills in seven areas north of the Yellow Sea boundary between the nations.

South Korea responded by returning fire after North Korean shells landed in its territorial waters.