A magnitude 3.4 earthquake has been detected in North Korea.

The earthquake occurred about 50km (31 miles) from a nuclear test site, monitors say. Previous quakes were caused by weapon tests.

Chinese seismologists initially said it was a “suspected explosion” but South Korea said it was likely a natural quake not caused by a nuclear test.

The US Geological Survey (USGS), meanwhile, said it could not yet make a judgment as to the cause.

North Korea carried out a massive nuclear test on 3 September which was widely condemned at the UN.

The size of Saturday’s tremor is smaller than the earthquakes registered as a result of all of North Korea’s six nuclear tests.

After the last test, which North Korea said was a hydrogen bomb, initial reports from the USGS put the tremor at magnitude 5.6 with a depth of 10km but this was later upgraded to magnitude 6.3 at 0km.

The latest quake was recorded at a depth of 0km in North Hamgyong province, home to the Punggye-ri nuclear site, South Korea’s meteorological agency says.

The USGS also said it occurred in the nuclear test area but said its seismologists assessed it as having a depth of 5km.

“We cannot conclusively confirm at this time the nature (natural or human-made) of the event,” it said.

While the cause remains unknown, alternative explanations suggested by North Korea analysts include tunnel collapses at the testing site possibly connected to the 3 September test.

South Korea said it believed the quake was natural because the specific soundwaves generated by artificial earthquakes were not detected, Reuters news agency reports.

Analysts from the Comprehensive Nuclear Test Ban Treaty Organization are examining the “unusual seismic activity of a much smaller magnitude” in North Korea, executive secretary Lassina Zerbo tweeted.

He said the quake occurred “about 50km from prior tests” and later added that two seismic events had been registered and it was unlikely they were “man-made”.

North Korea has refused to stop its missile and nuclear tests, despite successive rounds of UN sanctions and international criticism. Its leaders say nuclear capabilities are its only deterrent against an outside world seeking to destroy it.

On Saturday, China said it had moved to limit North Korea’s oil supply and would stop buying textiles from its traditional ally in line with the latest UN sanctions.

Earlier, Russian Foreign Minister Sergei Lavrov compared US President Donald Trump and North Korean leader Kim Jong-un to children fighting in a kindergarten.

The pair had swapped insults, with Mr Trump calling the North Korean a suicidal “rocket man” and being labelled “mentally deranged” and “a dotard” in return.