Story highlights North Korea proclaimed itself a "nuclear state" in a revised constitution this week

Analyst: Appears to be directed at the U.S. as the rhetoric from Pyongyang rises

Comes as signs are growing of activity at North Korea's nuclear test site

North Korea proclaimed itself a "nuclear state" this week following a revision of its constitution earlier this year.

Kim Jong-Il has "transferred the country into an undefeated country with strong political ideology, a nuclear power state, and invincible military power," according to the updated constitution posted on its portal website Naenara. The website posted the revised constitution on Wednesday, according to Yonhap, the South Korean state affiliated news agency.

The statement looks all too familiar.

North Korea previously announced its nuclear capability through its state-run broadcaster and newspapers, "but no expression can be stronger than including it in their constitution," Professor Choi Jong Kun of Yonsei University told CNN.

"It is an announcement of confirmation," he added, "and it appears to be directed to the U.S. and other relevant nations."

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The communist state carried out nuclear tests in 2006 and 2009.