Images surfacing show Kim Jong Un may be preparing a test, against UN sanctions
Kim Jong Un has made a defiant defence of his nuclear weapons programme at North Korea's first full congress of its ruling party since 1980.
It comes amid signs the isolated state is about to carry out another nuclear test, according to a US website that monitors the isolated nation.
In his opening address, Kim hailed the "magnificent... and thrilling" nuclear test carried out on January 6th, which Pyongyang claimed was a powerful hydrogen bomb.
The test and long-range rocket launch that followed a month later had "smashed the hostile forces' vicious manoeuvres geared to sanctions and strangulation, and displayed to the world the indomitable spirit, daring grit and inexhaustible strength of heroic Korea", Kim said.
North Korea has conducted a total of four nuclear tests, two of them since Kim came to power in late 2011 following the death of his father and former leader Kim Jong Il.
Speculation that the North might be about to make a fifth test, in defiance of UN sanctions, was fuelled by recent satellite imagery of a nuclear test site in the northeast of the country.
Analysts at the US-Korea Institute at Johns Hopkins University said the presence of vehicles at the complex's test command centre signalled the possibility of a test, is said to be "in the near future. While the historical record is incomplete, it appears that vehicles are not often seen there except during preparations for a test."
Most experts have doubted the North's hydrogen bomb claim.
However, they acknowledge the strides the North has made under Kim towards its ultimate goal of developing an inter-continental ballistic missile capable of striking targets across the US mainland.
The once-in-a-generation gathering of the country's top decision-making body is being scrutinised for signs of any substantive policy change or major reshuffle in the ruling elite.
The congress will elect its central committee which will in turn select a politburo, with Kim expected to bring in a younger generation of leaders picked for their loyalty.