South Korea-Japan relations have suffered a serious setback from revisionist acts by some Japanese politicians, the South Korean government said in an official document Friday.

In its 2015 Diplomatic White Paper, the Foreign Ministry described the problem as a "big obstacle" to improving the ties between Seoul and Tokyo.

"While Japan was engaged in brisk diplomatic activities (in 2014), advocating active pacifism, it caused conflicts with neighboring countries due to a revisionist move by some political leaders," it said.

The paper did not name those politicians, but many Koreans believe Prime Minister Shinzo Abe and his aides are trying to whitewash Japan's atrocities during World War II, including the sexual enslavement of Korean women, euphemistically called "comfort women."

South Korea and Japan have struggled to narrow differences over the comfort women issue. South Korea demands Japan's formal apology and reparations for the victims. But Japan claims it has no more legal responsibility.

On the Park Geun-hye administration's diplomacy, the document said the U.S. confirmed its support for Seoul's push for the "harmonious development" of its relations with Washington and Beijing.

As to North Korea, it said leader Kim Jong-un continued efforts in 2014 as well to solidify his power through the reign of terror.

The communist nation's economy failed to achieve substantive growth because of lack of fundamental reform measures, it added. (Yonhap)