A small artificial earthquake has been detected in North Korea, according to South Korean officials who say it was probably due to "blasting work".
Meteorological officials registered the 2.2 magnitude quake at 1230 local time (0330 GMT) around 34km (21 miles) south-east of the capital, Pyongyang.
A more powerful artificial earthquake was detected in January when the North conducted a nuclear test.
But officials say this is unlikely to be the result of a nuclear test.
South Korea's Yonhap news agency quoted one meteorological official as saying Wednesday's quake "is not believed to be the result of a nuclear test, considering its location or magnitude".
It had a depth of 1km at its epicentre indicating it may have been due to blasting work, reported the agency.
It follows an announcement by the North on Tuesday that it plans to conduct nuclear warheads tests, in the wake of some of the toughest sanctions yet imposed by the UN on North Korea.
On Monday North Korea saw a 3.3-magnitude quake. South Korean officials said indications showed that this was a naturally-occurring seismic shock.