Seoul: North Korea could conduct its fifth nuclear test before May, South Korean officials said on Sunday.
The flow of vehicles and personnel at the Punggye-ri base in the northeast of the country has increased recently, "about three or four times" compared to last month, Yonhap News Agency quoted the officials as saying.
They pointed out that a growing number of vehicles, which could carry nuclear energy technicians, have been seen going in and out of the tunnels which lead to the underground spaces where such type of tests are carried out.
These facts have led the Seoul government to assess that this is "a compelling signal that North Korea is preparing for its fifth nuclear test" and, therefore, the authorities are closely monitoring the situation in the neighbouring country.
Seoul had warned months ago of the possibility that Pyongyang might carry out a fifth atomic test.
The Pyongyang regime carried out nuclear tests in 2006, 2009, 2013 and most recently in January this year when it allegedly detonated a hydrogen bomb, though some experts have doubted the claim.
January's test was followed by the launch of a space rocket in February, suspected by the international community to be a covert missile test.
In response to both actions, the United Nations Security Council imposed harsher trade sanctions on Pyongyang, while South Korea, the US and Japan have declared unilateral measures in addition to trying to stifle North Korea's economy.