South Korea voiced "deep disappointment and regret" Tuesday over Japanese Prime Minister Shinzo Abe's ritual offering to a war shrine seen as a symbol of Japan's past militarism.

Abe sent a tree offering via his aide to Tokyo's Yasukuni Shrine earlier in the day as the country marked its two-day spring festival, Kyodo News reported.

"The government expresses deep disappointment and regret that Prime Minister Shinzo Abe has again sent an offering to Yasukuni Shrine, a symbolic establishment that beautifies Japan's colonial plunder and war of aggression," foreign ministry spokesperson Kim In-chul said in a commentary.

"The government strongly urges Japanese leaders to show their willingness to improve South Korea-Japan relations by acting to show they humbly reflect and repent for the past history while they properly face up to history."

Yasukuni Shrine honors Japan's war dead, including 14 Class A war criminals. Visits to the shrine by Japanese leaders have been a key source of tension in the region as Asian neighbors view the visits as an attempt to beautify the country's militaristic past.

Abe has not paid a visit to the shrine in person since his last visit in 2013 angered neighboring countries that suffered Japanese aggression in the early to mid-20th century, including South Korea and China.

He has instead sent an offering around key festivals and on Aug. 15, the anniversary of Japan's surrender in World War II.

Abe's offering comes as Japan is under a nationwide state of emergency due to the spread of the coronavirus outbreak. Last week, Abe expanded the state of emergency imposed on urban areas to across the country.

In contrast to past visits, a group of right-wing lawmakers from Japan's ruling and opposition parties decided not to visit the shrine during this festival, the first time since the group was founded in 1981, according to Kyodo. (Yonhap)