North Korea causes concern; images suggest nuclear test tunnel
Satellite images suggest North Korea is building a nuclear test tunnel that could be used for a detonation at its main nuclear test site.  Furthermore, South Korean and US intelligence now believe North Korea's claims that it has mastered the technology to produce a nuclear warhead small enough to be used with an intercontinental ballistic missile. North Korea had shut down its Yongbyon reactor in 2007 under a six-nation-aid-for-disarmament accord, however, it confirmed in September that it had resumed operations at the plant. Chinese experts believe North Korea had around 20 nuclear warheads at the end of 2014, which they say will double by the end of 2016. North Korea also intends to conduct nuclear tests and launch, what it claims, is a rocket to put a satellite into orbit, however, South Korea and the US say it would be disguised as a long-range missile test. They have both expressed "grave concern" over North Korea's test plans and urged the country to cease all activities.

Satellite photographs from October and early November indicate North Korea is digging a new tunnel for nuclear testing, a US research institute said on Wednesday.

A report on 38 North, a North Korea monitoring website run by Johns Hopkins University’s school of advanced international studies in Washington, said the images showed significant construction since April at Punggye-ri, on North Korea’s east coast, where three previous nuclear tests were conducted.

However, there are no signs any testing is imminent, it said.

The commercial images showed excavation of a new tunnel in addition to the three others where North Korea has either conducted nuclear tests or excavated tunnels in the past, the report said.

The report said: “While there are no indications that a nuclear test is imminent, the new tunnel adds to North Korea’s ability to conduct additional detonations at Punggye-ri over the coming years if it chooses to do so.”

On 30 October, South Korea’s Yonhap news agency quoted a South Korean government source as saying there was active movement of workers and vehicles working on a new tunnel at the site.

The source said this indicated an intention to conduct a nuclear test “at some point”, though this did not appear to be imminent.

North Korea conducted its last nuclear test in 2013, drawing international condemnation including from China, its main diplomatic ally. North Korea is under United Nations sanctions that ban trade that can fund its arms program.

Pyongyang has vowed to continue to conduct nuclear tests and to launch what it says is a rocket to put a satellite into orbit, something South Korea and its main ally, the US, say would be a disguised long-range missile test.

American and South Korean defence chiefs have expressed “grave concern” over North Korea test plans and urged it to cease all activities related to its nuclear programme immediately.