SEOUL, South Korea — In a significant step toward overcoming lingering historical animosities with its former colonial master, the South Korean government has unexpectedly announced that it will sign a treaty with Japan on Friday to increase the sharing of classified military data on what analysts cite as two major common concerns: North Korea’s nuclear and missile threats and China’s growing military might.
The announcement set off a political firestorm in South Korea, where resentment of Japan’s early 20th-century colonization remains entrenched and any sign of Japan’s growing military role is met with deep suspicion. The opposition accused President Lee Myung-bak of ignoring popular anti-Japanese sentiments in pressing ahead with the treaty, the first military pact between the two nations since the end of colonization in 1945.
North Korea accused Mr. Lee’s government of “selling the nation out.”
The accord, the General Security of Military Information Agreement, provides a legal framework for South Korea and Japan to share and protect classified and other confidential data. Cho Byung-jae, the spokesman of the South Korean Foreign Ministry, said the South Korean ambassador to Tokyo, Shin Kak-soo, and Japan’s foreign minister, Koichiro Gemba, plan to sign the treaty on Friday, after the Japanese cabinet’s approval.
The United States has been urging the two countries to strengthen military ties, so the three nations can deal more efficiently with threats from North Korea.
It was well known that South Korea and Japan, which enjoy thriving economic ties and cultural exchanges, were negotiating the deal, but the opposition and other government critics here were caught off guard by Thursday’s announcement because earlier indications had been that historical hostilities would again delay a pact. The two remain locked in disputes over the ownership of a set of islets and over Tokyo’s rejection of talks on compensating “comfort women,” Koreans the Japanese military forced into sexual slavery during World War II.
Military cooperation between the two has lagged, although a cautious military rapprochement sped up after North Korea’s artillery bombardment of a South Korean island in 2010. China’s naval expansion has also prompted politicians in the two countries to call for closer military ties. In the past week, the United States, Japan and South Korea conducted a joint naval exercise in the seas south and west of the Korean Peninsula.
Officials here said the need for the allies to share data on bellicose and enigmatic North Korea has grown with the increased uncertainty after the death of its longtime ruler, Kim Jong-il, in December.
Under the rule of his son Kim Jong-un, North Korea has vowed to bolster its production of nuclear weapons. It launched a rocket in April, and although it failed to put a satellite into orbit, Washington condemned the launching as a test of intercontinental ballistic missile technology.
The political opposition and several civic groups in South Korea warned that the new military cooperation deal would only intensify regional tensions and encourage Japan’s “militaristic ambition.” “When the Lee Myung-bak government started out, it was pro-American to the bone, and as it nears the end of its term, it is proving pro-Japanese to the bone,” said Park Yong-jin, spokesman of the main opposition Democratic United Party.
Mindful of such a political offensive, Hwang Woo-yea, the head of the governing New Frontier Party, visited the disputed islets in the sea between South Korea and Japan on Thursday in a symbolic gesture reconfirming South Korea’s territorial claim.
“Every grain of sand here, every rock here, belongs to South Korea,” he told South Korean police officers guarding the islets.