SEOUL (AFP) - South Korea slammed Japanese Prime Minister Shinzo Abe on Thursday for sending a message of support earlier this year to a memorial service dedicated to World War II war criminals.

The message has raised "doubts about the sincerity of apologies over (Japan's) wartime atrocities and colonial rule", Foreign Ministry spokesman Noh Kwang Il told reporters. "We have no choice but to express deep concerns over Abe's repeated remarks and behaviours which can be seen as denying the post-war order," he said.

In April, Mr Abe sent his message to a memorial service at a temple in western Japan to commemorate wartime leaders, including class-A war criminals, organisers of the ceremony said on Wednesday.

Mr Abe reportedly said in his message: "I express my grief at the death of martyrs... who sacrificed their lives to form the foundation of peace and prosperity in Japan today."

Relations between Tokyo and Seoul are at their lowest ebb in years over disputes related to Japan's 1910 to 1945 colonial rule over the Korean Peninsula.

The two main US military allies in Asia are also mired in a territorial row over a tiny batch of rocky islets in the East Sea (Sea of Japan).

South Korea feels Japan has not gone far enough in expressing remorse for the abuses of the colonial period or in compensating its victims.

China also reacted angrily to the news of Mr Abe's message to the memorial service, castigating his "incorrect attitude" to the past.