"The U.S. government on Friday hailed Japan's new security strategy as a "bold and historic" step to help maintain peace in the Indo-Pacific, with the key Asian ally forging ahead with its biggest defense buildup plans since World War II amid China's rise and North Korean threats.

In a major shift in its security policy under its pacifist Constitution, the Japanese government decided to acquire strike capabilities that could potentially reach an adversary's territory and set a target of doubling its annual defense budget to about 2 percent of its gross domestic product over the next five years.

The moves were welcomed with effusive praise from the U.S. administration of President Joe Biden, which views China as posing increasing challenges to the rules-based international order, while defense experts in the United States noted the "hard work" of following through on the commitments.

Calling the U.S.-Japan alliance "the cornerstone of a free and open Indo-Pacific," Biden tweeted, "We welcome Japan's contributions to peace and prosperity."

White House National Security Adviser Jake Sullivan said in a statement that Japan has taken "a bold and historic step to strengthen and defend the free and open Indo-Pacific with the adoption of its new National Security Strategy" and two other related defense documents.

U.S. Defense Secretary Lloyd Austin expressed support for Japan's decision to acquire the so-called counterstrike capabilities, saying the move will "strengthen regional deterrence" while committing to working with Japan to support the goals enshrined in both countries' strategies.

Japan's National Defense Strategy, which was revamped along with its National Security Strategy for the next decade, has an "important alignment" with a corresponding U.S. document, Austin also said, pointing out that both seek to modernize the alliance, bolster deterrence and address security challenges through cooperation with like-minded allies and partners.

U.S. Secretary of State Antony Blinken said Japan's new documents "reshape" the ability of the alliance to promote peace in the region, and called Japan an "indispensable partner" in dealing with the most pressing challenges to global stability including Russia's invasion of Ukraine that began in February.

James Schoff, a former senior adviser for East Asia policy at the Pentagon, said Russia's war and China's military buildup, combined with the consolidation of President Xi Jinping's political power, have driven Japan toward the latest decision, with a goal of "discouraging Beijing from thinking that use of military force can help it achieve what it wants around Japan."

Japan has been hardening its stance toward China as Beijing has stepped up its territorial claims in neighboring waters and its pressure against Taiwan. China views the self-ruled democratic island as a renegade province to be reunified with the mainland, by force if necessary.

A Taiwan contingency, which could draw the United States into a conflict with China, is a concern for Japan, given the close proximity of its southwestern islands -- including the Senkakus, a group of East China Sea islets controlled by Tokyo but claimed by Beijing.

Japan itself could become the target of an attack in such a conflict, as it hosts bases the U.S. military would rely on for executing operations.

Under Japan's new defense buildup program, it plans to procure U.S.-made long-range Tomahawk cruise missiles, which could be used for developing counterstrike capabilities.

Schoff, currently senior director at the Sasakawa Peace Foundation USA in Washington, said he believes Japan's planned acquisition of the new capabilities are aimed at "being able to hit Chinese ships and planes from far away" rather than any desire to be able to strike "deep into China's mainland."

What would be noteworthy is that the expected increase in Japanese capability and sophistication in defense missions -- including through counterstrike systems, active cyber defense and improved readiness of the Self-Defense Forces -- should lead to greater integration of U.S. and Japanese planning, intelligence and information sharing, he said.

But Schoff acknowledged that efficiently and effectively beefing up Japan's defense power as pledged "will not be easy" and "there is no guarantee that Japan will fulfill all this potential."

Joseph Nye, a former U.S. assistant defense secretary for international security affairs, described Japan's defense buildup moves as "healthy," but indicated that Japan's possession of counterstrike capabilities in itself would not necessarily dissuade China from a possible invasion of Taiwan.

"Japan can't deter China (alone). What deters China is the fact that the U.S. and Japan are closely aligned," he said.

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