North Korea could be preparing to carry out a fourth nuclear test, South Korea says, citing increased activity at its main test site just days ahead of a visit to Seoul by US President Barack Obama.
"Our military is currently detecting a lot of activity in and around the Punggye-ri nuclear test site," defence ministry spokesman Kim Min-Seok told a press briefing on Tuesday.
Kim stressed that North Korea's nuclear weapons program was at a stage where it could conduct a test "at any moment" once the order was given by the leadership in Pyongyang.
North Korea has conducted three nuclear tests - in 2006, 2009 and 2013 - all at the Punggye-ri site in the northeast of the country.
Kim declined to give details of the monitored activity, but cautioned that it may be no more than a "deception tactic" to raise tensions ahead of Obama's visit which is due to begin on Friday.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Obama is visiting Seoul as part of an Asia tour, and there has been widespread speculation that the North may stage a provocation to coincide with the trip.
On Monday, Pyongyang slammed Obama's upcoming trip as a "dangerous" move that would escalate military tension and bring the "dark clouds of a nuclear arms race" over the Korean peninsula.
Several analysts said they were sceptical that North Korea would carry out a test at the current time, and said Pyongyang was just seeking to rattle a few cages.
Professor Yang Moo-Jin of the University of North Korean Studies in Seoul, said a test now would risk permanently alienating the North's only major ally and chief economic benefactor, China.
A nuclear test would also extinguish any chance of a resumption of six-country talks on North Korea's nuclear programme that China has been pushing for.
