A five-day air combat exercise by Japan's Self-Defense Forces and United States troops based in Japan has ended, as the two ally countries prepare for deliberations to revise their security cooperation treaty.

The drill was conducted over Pacific waters on Tuesday off the coast of Shikoku, the fourth-largest of Japan's islands, with four F-4 fighter jets and an unspecified number of personnel from JASDF and six FA-18 fighters and some 90 soldiers from the US, according to Japan's NHK.

Foreign affairs and defense officials from the two countries are scheduled to begin discussions on a revision to the guidelines for their defense cooperation on Thursday.

Amid China's maritime activities and military capabilities, the discussions will focus on how the revised guidelines should define the roles to be shared by Japan and the US in terms of intelligence, surveillance and reconnaissance, according to Japan's Jiji Press.

Japanese Prime Minister Shinzo Abe has repeatedly emphasized the need to exercise the right to collective self-defense in rebuilding the Japan-US alliance, and this topic will also be demonstrated in the discussions on Thursday, according to the Kyodo News Agency.

The Diaoyu Islands dispute and Pyongyang's rocket launch offer Japan excuses to enhance its collective self-defense, which allows Japan to help defend US troops when necessary, said Wang Ping, a researcher on Japanese studies with the Chinese Academy of Social Sciences.

Exercising the right to collective self-defense with the US means the two countries will have an equal military position, but the US is not eager to see this happen, Wang said.

Faced with pressure over a shrinking military budget, the US expects its allies in the Asia-Pacific to contribute more to its pivot to the region, which is why Washington wants to discuss the security cooperation treaty with Japan, said Pang Zhongying, a professor on international affairs with Renmin University of China.

But the US knows that Japan's right to exercise collective self-defense is a double-edged sword, and may also pose a threat to Washington's interests in the region, so the US will also take precautions against Japan, he said.

Japan has beefed up measures to strengthen the US-Japan military alliance.

Japan's Self-Defense Forces launched a military drill on island defense at a training ground in the city of Narashino, Chiba prefecture, on Sunday.

The war game was played under the scenario that a Japanese islet was captured by enemy forces, and airborne forces retook the island with the help of maritime and air forces.

Meanwhile, China is beefing up maritime and air patrols of the Diaoyu Islands in the East China Sea as part of its law enforcement and jurisdiction practices.

Mapping of islands

In a separate development, China is to survey the Diaoyu Islands as part of a mapping program of its territorial islands and reefs, according to Xinhua News Agency.

The Diaoyu Islands and the nearby waters are China's inherent territory, and the purpose of surveying the islands is to safeguard China's maritime rights and interests, Chinese Foreign Ministry spokesman Hong Lei said at on Tuesday.

The first stage of the island surveying and mapping was launched in 2009 and has finished the monitoring of islands located within 100 km of the coastline, according to a document issued at a news conference by the National Administration of Surveying, Mapping and Geoinformation.

The second stage will cover islands including the Diaoyu Islands, the document said.

It added that this program is part of the country's efforts to safeguard its maritime rights and interests.

By the end of last year, China had completed the identifying and precise positioning of about 6,400 islands and more than 4,900 island maps of three scales.

Contact the writers at caihong@chinadaily.com.cn and zhouwa@chinadaily.com.cn

Xinhua contributed to this story.