In its updated global defense strategy, the Pentagon on Tuesday emphasized the need to counter a "significant" threat from North Korea's unpredictable regime.

"North Korea remains closed and authoritarian," it said in the 2014 Quadrennial Defense Review, which Defense Secretary Chuck Hagel characterized as defining the "historic transition" unfolding through the U.S. defense enterprise.

The QDR sets the direction of the U.S. military's overall operations at home and abroad in a period of budget austerity.

The Pentagon said the U.S. military will be reduced in size but will become "more modern and more ready to confront a broad range of future defense challenges."

It pointed out North Korea's nuclear and long-range missile capabilities are a "growing and direct" threat to the U.S. and its allies.

"North Korea's long-range missile and weapons of mass destruction programs -- particularly its pursuit of nuclear weapons in contravention of its international obligations -- constitutes a significant threat to peace and stability on the Korean Peninsula and in Northeast Asia and is a growing, direct threat to the United States," the review said.

The 88-page document, issued along with the U.S. military's fiscal year 2015 budget request, describes the communist nation and Iran as sources of "dynamic and unpredictable" challenges.

"Faced with this threat, the United States is committed to maintaining peace and security on the Korean Peninsula and closely monitors the situation through military and diplomatic channels in coordination with the ROK, Japan, China and Russia," it said. ROK is the acronym for South Korea's official name, the Republic of Korea.

The department said it would continue efforts to stay ahead of the North's ballistic missile threats.

The Pentagon plans to build out U.S. homeland defense with 44 Ground-Based Interceptors by 2017.

It will also procure an additional Terminal High-Altitude Area Defense battery in 2015, bringing the total number of batteries to seven.

The Pentagon also said the Marine Corps is committed to remaining the country's "expeditionary force: a force capable of responding to crisis anywhere around the globe at a moment's notice."

On the Obama administration's broader policy of rebalancing toward Asia, it vowed to maintain a "robust footprint in Northeast Asia" while enhancing its presence in Oceania and Southeast Asia.

The QDR said what is also worrisome is the rapid pace and comprehensive scope of China's military modernization, combined with a relative lack of transparency and openness from China's leaders regarding both military capabilities and intentions.

"In the coming years, countries such as China will continue seeking to counter U.S. strengths using anti-access and area-denial approaches and by employing other new cyber and space control technologies," it said.

Meanwhile, Hagel said in a statement the QDR "outlines key missions of our strategy -- including the rebalance to the Asia-Pacific, sustaining our security commitments in the Middle East and Europe, and building partnership capacity throughout the world."

He emphasized that his department is doing its best to adapt itself to budget reductions but that there would be serious consequences should the sequester of automatic budget cuts persist.

"The QDR shows that continued sequestration requires dangerous reductions to readiness and modernization," he said. (Yonhap)