A former American lawmaker Tuesday urged Japanese Prime Minister Shinzo Abe to apologize, in unequivocal terms, to "comfort women", a euphemism for sex slavery, procured for wartime Japanese military brothels if he is to deliver a speech at a joint session of the US Congress.

In an article contributed to the newspaper Hill, Eni Faleomavaega, who retired this year after serving for 25 years as a member of the House of Representatives, said the House chamber where Abe could make a speech, is where a landmark 2007 House resolution on sexual slavery victims passed.

He noted that it is also the place President Franklin Roosevelt gave his renowned speech the day after the 1941 Pearl Harbor attack.

Faleomavaega stressed that "it would be only fitting and proper for Abe to bring a final closure to certain historic issues regarding the Second World War" if he is invited to speak in a chamber of historic significance.

The ex-lawmaker went on to say that Abe could make use of his visit to the American Congress to "formally acknowledge, apologize, and accept historic responsibility in a clear and unequivocal manner for the historic human rights violations committed against the comfort women."

Besides, Abe could also reaffirm the Murayama Statement, the statement of apology Japan made in 1995, where the country apologized for its imperialistic past. The nationalist prime minister has also been accused of trying to revise the apology statement.

German Chancellor Angela Merkel, who left Japan in the afternoon after a two-day visit, her first to the country in seven years, also called for an early settlement of the sensitive issue during a meeting with Katsuya Okada, head of the main opposition Democratic Party of Japan, in Tokyo.

Japan invaded northeast China in 1931 and mounted a full-scale invasion in 1937. By the end of World War II, more than 35 million Chinese were killed or wounded during the Japanese aggression.

However, Japanese rightists are trying to deny and whitewash the country's wartime atrocities, including the Nanjing Massacre and the issue of "comfort women," which involves forcibly recruiting and coercing women to serve the Japanese Imperial Army during the war.