North Korea is ready to launch a nuclear test, according to a US-based North Korea monitoring project.
The 38 North group described the Punggye-ri Nuclear Test Site as "primed and ready."
"Commercial satellite imagery of North Korea's Punggye-ri Nuclear Test Site from 12 April shows continued activity around the North Portal, new activity in the Main Administrative Area, and a few personnel around the site's Command Centre," the 38 North website said.
A barrage of recent North Korean missile tests has stoked US fears that North Korea may soon develop an intercontinental ballistic missile capable of delivering a nuclear warhead to the US mainland.
There is speculation that the country could be preparing a missile launch or another nuclear test - its sixth - to mark the 105th anniversary of the birth of its founder Kim Il-Sung on Saturday.
German Chancellor Angela Merkel has urged the US and China to put political pressure on North Korea over its nuclear programme, pressing for a peaceful resolution to escalating tensions.
In comments released today, Ms Merkel said: "I don't put my trust in military means, but rather in political pressure being exerted on North Korea from different sides."
Yesterday, Chinese President Xi Jinping called for a peaceful resolution of rising tension on the Korean peninsula in a telephone conversation with US President Donald Trump, as a US aircraft carrier strike group heads towards the region.
The strike group, headed by the USS Carl Vinson, is still some way south conducting exercises with the Australian navy.
The US Navy already has a massive regional presence, including another carrier strike group headquartered at Yokosuka in Japan.
