The US President Barack Obama says a reclusive North Korea poses a threat not just to the Asian region, but to the United States.
President Obama’s arrival in South Korea on Friday comes amid growing signs that the North is preparing a nuclear test.
While stressing that Washington stands should-to-shoulder with Seoul, Mr Obama says Pyongyang will “gain nothing” by making threats.
“Threats will get North Korea nothing, other than greater isolation,” Obama said at a joint press conference with South Korean President Park Geun-Hye.
Both the United States and South Korea have repeatedly called on China to use its political and economic influence and exert more pressure on North Korea to give up its nuclear weapons programme.
“China is beginning to recognise that North Korea is not just a nuisance but a significant problem for their own security,” he said.
South Korean officials have gathered intelligence that shows all the technical preparations have been completed for Pyongyang to conduct its fourth nuclear test.
A North American think tank says new satellite photos also show additional activity at the Punggye-ri test site that is “probably related to preparations for a detonation”.
The US-Korea Institute at Johns Hopkins University says the latest images suggest increased movement of vehicles and materials near what are believed to be the entrances to two completed test tunnels.
Also visible were probable command and control vehicles intended to provide secure communications between the test site and other facilities.
The report echoed recent warnings from South Korea that the North might be planning a test to coincide with Mr Obama’s two-day visit.
In an interview ahead of his arrival in Seoul, Mr Obama warned North Korea could expect a “firm response” if it made “the mistake” of conducting another nuclear test.
Last month North Korea threatened to conduct a new type of nuclear test, referring to an explosion with enriched uranium.
North Korea has conducted three nuclear tests in 2006, 2009 and 2013.
