"For a complete solution of the North Korean nuclear issue, which creates tension on the Korean Peninsula, it is necessary to unite North and South," Oh said Tuesday during a lecture at New York University, as quoted by the Yonhap news agency.
Oh added that reunification would constitute "a complete resolution of the North Korean nuclear problem."
South and North are still formally at war, as no peace treaty has been signed after the Korean War of 1950-1953.
North Korea declared itself a nuclear power in 2005 and conducted nuclear tests in 2006, 2009 and 2013, having earlier withdrawn from the Nuclear Non-Proliferation Treaty that it ratified in 1985.
The United States, Japan and South Korea, as well as Russia and China, took part in talks on denuclearization of the Korean Peninsula with North Korea from 2003 until 2009, as Pyongyang withdrew from the talks.
