Kim Jong-Un on Friday opened North Korea’s first ruling party congress for nearly 40 years with a defiant defense of the "magnificent" strides made in the country’s nuclear weapons program.

Kim Jong-Un on Friday opened North Korea's first ruling party congress for nearly 40 years with a defiant defense of the "magnificent" strides made in the country's nuclear weapons program.

Hailing the historic test of what North Korea claims was a hydrogen bomb in January, the isolated state's young leader said it had shown the world it would not be cowed by sanctions or outside pressure.

Dressed in a western style suit and tie, Kim's speech was delivered to thousands of party delegates who had gathered in Pyongyang for the once-in-a-generation conclave.

In particular, he praised the country's scientists for "creating milestone miracles with the magnificent and exhilarating sound of the first H-bomb of our republic".

The test and successful long-range rocket launch a month later "clearly demonstrated to the whole world our undefeatable spirit and endless power ... in defiance of malicious pressure and sanctions by enemy forces," he said.

His speech, shown late Friday on state TV, was frequently interrupted by thunderous applause and at last one standing ovation.

Most experts have questioned the North's H-bomb claim, saying the detected yield from the January test was far too low for a full-fledged thermonuclear device.

There has been widespread speculation that the North might have prepared another nuclear test to coincide with the congress, as a defiant gesture to underscore its nuclear power status.