South Korea expressed "deep regret" Monday after former Japanese Prime Minister Shinzo Abe again visited a war shrine, urging Tokyo to atone for its colonial-era atrocities through action.

Abe's visit to the Yasukuni Shrine in Tokyo earlier Monday was his second since he stepped down as prime minister in mid-September due to health problems.

"We express deep concern and regret that responsible leaders of Japan are visiting the Yasukuni Shrine, a symbolic establishment that beautifies (Japan's) colonial plunder and war of aggression," a Seoul foreign ministry official said, citing the ministry spokesman's statement following Abe's previous visit on Sept. 19.

"The government once again sternly points out that the international community can trust Japan only when these leaders squarely face history and demonstrate their humble reflections and sincere atonement for past history through action," the official added.

Yasukuni Shrine honors Japan's war dead, including 14 Class A war criminals. 

Abe refrained from visiting the shrine for nearly seven years while in office, apparently to avoid angering neighboring countries, and instead sent offerings around key festivals and anniversaries.

Many South Koreans harbor deep resentment over Japan's brutal colonial rule of the Korean Peninsula from 1910-45. (Yonhap)