Photo/IllutrationHiroshi Imazu, second right, chair of the Research Commission on Security for the Liberal Democratic Party, submits a proposal on missile defense to Prime Minister Shinzo Abe, right, flanked by former Defense Minister Itsunori Onodera, second left, head of the LDP panel, at the prime minister's office in Tokyo on March 30. (AP Photo/Pool)

Japan's ruling party urged the government Thursday to consider arming itself with more advanced and offensive capability, such as striking enemy targets with cruise missiles, further loosening the self-defense-only military posture the country has had since the end of World War II.

The Liberal Democratic Party's council on defense policy urged the government in Tokyo to immediately start studying ways to bolster Japan's capability to intercept missiles with a system such as the Terminal High-Altitude Area Defense, or THAAD system, that the U.S. and Seoul have agreed to install in South Korea.

The panel cited a "new level of threat" from North Korea, which fired four missiles this month, three of them landing inside Japan-claimed exclusive economic waters.

"North Korea's provocative acts have reached a level that Japan absolutely cannot overlook," the party's security panel said in the proposal given to Abe. "We should not waste any time to strengthen our ballistic missile defense."

The panel said the government should immediately start studying a possibility of introducing THAAD and the shore-based Aegis missile defense system, among other equipment, while pursuing upgrades to two existing missile defense systems--ship-to-air SM-3 interceptors and the ground-based PAC-3.

Japan is bound by its postwar pacifist Constitution, and the proposal does not call for a first-strike capability. Japan since its World War II defeat has limited its military to self-defense, while relying on the U.S. "nuclear umbrella" and its 50,000 troops stationed in Japan under a bilateral security alliance as deterrence.

But Abe has started stretching those restrictions since taking office in 2012 by easing a self-imposed ban on weapon exports and enacting legislation that reinterprets the war-renouncing Constitution to allow Japan's military to defend allies under attack.

Japan's defense budget has steadily risen over the past five years under Abe, who ended a decade of defense budget cuts. The annual increase is currently just over 2 percent, and Abe says he is ignoring a customary cap of 1 percent of GDP.

The panel noted that North Korea's test-firing of missiles in the past year demonstrates advancing technology, with a capability to launch from a mobile facility or submarine, use solid fuel, as well as fired to a high-altitude trajectory--which makes it harder to trace and respond.