In a sign of the deep-seated rancor between Seoul and Tokyo, more South Koreans would back their neighbor to the north if it went to war with Japan, according to a new survey by a state-sponsored think tank in Seoul.

The survey, conducted by research fellow Lee Sang Sin, was presented Wednesday as part of the Korea Institute for National Unification's 11th annual Peace Forum, and comes amid increasingly fraught ties strained by rows over trade and history.

"Under a rather extreme hypothetical situation in which war may break out between North Korea and Japan, 45.5 percent would choose to help North Korea, and 15.1 percent Japan," the survey showed. About 39.4 percent responded that they "have no idea."