SEOUL, April 27 -- Four South Korean civic groups urged Japanese Prime Minister Shinzo Abe Monday to make a sincere apology for wartime crimes of the past on the occasion of his historic speech to a joint session of the U.S. Congress scheduled for Wednesday.

A total of 68 members of four civic organizations, including the Korean Women's Bar Association and the People's Solidarity for Participatory Democracy, sent a joint letter to heavyweight U.S. politicians such as U.S. Vice President Joseph Biden and House of Representatives Speaker John Boehner as well as Mark Lippert, U.S. ambassador to Seoul.

The letter delivery came as Abe is scheduled Wednesday to become the first Japanese prime minister to address the joint meeting of the U.S. Congress.

The letter urged members of the U.S. Congress to "urge Mr. Abe to voice clearly and publicly a heartfelt apology for its colonial rule and aggression, including military sexual slavery known to the world as comfort women."

It said that the comfort women victims, forced into sexual slavery for the Japanese military brothels during World War II, " are passing away one by one" for their old age.

There are only 53 South Korean victims alive, who identified themselves as former sex slaves, out of an estimated 200,000 comfort women victims, mostly from the Korean Peninsula.

Twenty-four House of Representatives lawmakers, led by Mike Honda, sent a letter to Japan's ambassador to the U.S. last Thursday, urging Abe to address its wartime wrongdoing during his upcoming speech.

Abe, however, is highly unlikely to express his remorse in the speech for "colonial rule and aggression" and forced recruitment of sex slaves by the imperialistic "Japanese government" given his recent remarks and attitudes.

A week earlier, Abe said in his appearance on a Fuji TV program that there would be no need to repeat apologies made by his predecessors, including the 1995 Murayama statement.

Abe made a ritual offering last week to the notorious Yasukuni Shrine, a symbol of Japan's militaristic past as the shrine honors about 2.4 million Japanese war dead, including 14 Class-A war criminals.