Japan highlighted China as a major security threat in its latest defense white paper released on Tuesday, using harsher language than in previous papers.

Observers said that by describing the security environment as increasingly severe, Tokyo has given itself an excuse to accelerate its military buildup and strengthen the Japan-US defense relationship.

In addition to the issue of the Democratic People's Republic of Korea's nuclear program, China was once again blamed in the annual report for expanding its maritime presence.

Mentioning the ongoing tension over the Diaoyu Islands in the East China Sea, the document said some of China's regular patrol activities in the relevant waters and airspace were "dangerous actions that could cause a contingency and are extremely regrettable".

Compared with last year's white paper, this year's edition elaborates on the protection of the remote offshore islands. For the first time, the document discloses Tokyo's detailed combat contingency plans for handling territorial disputes.

Wang Ping, a researcher on Japanese studies at the Chinese Academy of Social Sciences, said the Japanese military has been running a scenario of retaking remote islands to win more public support for lifting restrictions on the country's armed forces.

"The security issue may be a preferred option now for the ruling party to gain voters' support in the upcoming upper-house elections later this month, because many Japanese are not interested in the proposals for revising the pacifist constitution," Wang said.

According to the contingency plans unveiled by the white paper, "If signs of attack are detected in advance, Self-Defense Forces troops will be concentrated in the expected area before the enemy units' deployment and try to deter enemy attacks."

Retaking islands

But if no signs of aggression are detected in advance and the islands are occupied, operations will be conducted to regain the islands by defeating the enemy with air-to-ground and ship-to-ground strikes and by landing of ground SDF units, it said.

Jiang Xinfeng, an expert on Japanese studies at the PLA Academy of Military Science, said the Japanese military has gradually shifted its defense focus to China in recent years amid the ups and downs of the East China Sea situation.

"Tokyo's military deployment has shown great emphasis on the offshore islands in the southwest. 'Defending and retaking' them has been highlighted as a major pattern of a possible military operation," Jiang said.

The China-Japan relationship became strained last September after the Japanese government illegally nationalized part of China's Diaoyu islands in the East China Sea.

Patrol ships sent by China Marine Surveillance enhanced law enforcement in the waters off the islands last year, over which Tokyo has expressed discontent and panic.

Beijing said on Tuesday that China's regular maritime practices are "beyond questioning", a response to Tokyo's allegation that Beijing is operating in contravention of international law.

The annual report said, "China has attempted to change the status quo by force based on its own assertion, which is incompatible with the existing order of international law," and "China should accept and stick to the international norms".

China has been consistently seeking a resolution for territorial and maritime disputes through dialogue and reconciliation, Chinese Foreign Ministry spokeswoman Hua Chunying told a daily news conference.

"China, in the meantime, never allows any country to infringe on its territorial sovereignty," Hua warned.

In February, the Japanese defense minister accused a Chinese warship of locking its fire-control radar onto a Japanese vessel but Beijing soon rejected the allegation, saying the facts did not support the claim.

However, the Tuesday report once again mentioned the so-called radar incident, repeating Tokyo's accusations.

"Japan's security environment is surrounded with destabilizing factors, some of which are becoming increasingly tangible, acute and serious," said Masayoshi Tatsumi, defense councilor of Japan's Ministry of Defense at a briefing before the cabinet's approval of the white paper.

"The first budget hike in 11 years" is a common catchphrase in the annual report, a fact that analysts say reflects the military ambitions of the Liberal Democratic Party, which regained a majority in the lower house last year, and which seems to be pushing for a military buildup.

Military buildup

Japan's defense budget for the 2013 fiscal year, approved by the Abe cabinet in January, rose 0.8 percent to 4.68 trillion yen ($51.7 billion), the first increase in the past 11 years.

Meanwhile, the Japanese Defense Ministry is considering purchasing two Aegis-quipped destroyers to bring its total number of the missile-defense vessels to eight, in the light of the continuing threats from the DPRK, Japan's Kyodo News reported.

Zhou Yongsheng, an expert on Japanese studies at China Foreign Affairs University, said Tokyo has chosen to hype the supposed threat from China as "a bargaining chip" to neutralize domestic resistance to its military expansion plan.

Japan has lately strengthened monitoring operations on the East China Sea with more satellites, and "it has not changed its intention to rein in China", Zhou warned.

"Recently, Japan has frequently hyped China's 'threat' to deliberately inflame tensions, and some political forces take it as an opportunity to campaign for a military buildup and war-time preparations," said Hua, the Foreign Ministry spokeswoman.

Japan's maritime Self-Defense Force currently deploys four Aegis destroyers that are capable of intercepting a ballistic missile with the sea-based Standard Missile-3, and is renovating two other Aegis destroyers to be ready by 2018.

Japan announced in 2010 that it was shifting from a static defense, which rests on mobilization, to a "dynamic defense" that requires more agile forces, able to operate in the air and maritime regions bordering Japan.

The latest white paper endorsed the traditional US-Japan military alliance, but it also expressed concerns over Washington's decision to further cut its own defense budget, asking Tokyo to shoulder more of the financial burden.

Japan had made efforts to strengthen the military bond by holding a summit between US President Barack Obama and Japanese Prime Minister Shinzo Abe, and meetings between their defense ministers this year, the annual report said.

The Japan-US defense cooperation has covered all fields, including joint drills, cooperative development of SM-3 block IIA ballistic missile defense and placing US TPY-2 radars in Japan.

"Although Tokyo has been seeking greater independence in the defense arena, its defense independence remains limited in the framework of US-Japan military alliances," said Wang of the CASS.

The US is offering training for a 700-strong force for ground troops from Japan's SDF, who have been on joint US-Japan military exercises, the white paper said.