In the letter to the mayor of the northern Polish city of Gdansk, the Nobel laureate said: "This silence can be considered a mistake ... it can also be condemned." Grass is an honorary citizen of Gdansk.

Earlier revelations that Grass had served in the Waffen SS at age 17 were followed by calls by some politicians, including former Polish president Lech Walesa, to strip him of his honorary citizenship in the city.

In the letter to Mayor Pawel Adamowicz, Grass wrote that only in his old age has he found the "right formula" to talk about having served in the SS. Adamowicz had written to Grass asking him asking for an explanation.

The letter was read out Tuesday during a news conference in Gdansk, where Grass was born in 1927 when it was known as Danzig, and mainly inhabited by Germans.

Walesa, who is also an honorary citizen of Gdansk, responded by saying he was dropping his demand that Grass give up his honorary citizenship. The former leader of Poland's anti-communist Solidarity trade union movement said: "This letter has convinced me and from this moment, I am no longer in conflict with Mr. Grass. I think he's explained himself sufficiently."

Grass wrote: "In my blindness as a boy of 15, I applied to serve on submarines, but I was not accepted. But in September 1944, at the age of 17, I was conscripted into the Waffen SS, without having a say."

The German novelist, who won the Nobel Prize for literature in 1999, added: "It's only now, with age, that I have found a suitable way of talking about it from a wider perspective."

"I would however like to maintain the right to affirm that I have learned the painful lesson that life gave me in my youth. My books and my political activity are testimony to that."

Grass, 78, revealed his SS past earlier this month, stunning Germans and drawing criticism in Poland, which was invaded by Nazi Germany in World War II.

Poland's ruling Law and Justice party has called on the Gdansk city authorities to revoke Grass' honor. But a number of prominent figures in Poland have rallied to Grass's defense, including Adam Michnik, the editor in chief of the influential Gazeta Wyborcza daily, and Archbishop Jozef Michalik, president of the Polish episcopate.

Grass rose to fame with the publication in 1959 of "The Tin Drum," which examined Germany's Nazi legacy.