Prominent German writer Gunter Grass confronts Israeli policy in a new poem lauding Mordechai Vanunu, a former nuclear technician imprisoned by Israel for years for revealing details of Israel's nuclear program to the British media.

In April, Israel declared the Nobel Prize literature laureate Grass "persona non grata" after he published a poem saying Israel threatened world peace in its standoff with Tehran and that it must not be allowed to launch military strikes against Iran.

Grass' words were also denounced by mainstream political parties in Germany, where any strong condemnation of Israel is taboo.

In a new poem, the German writer calls Vanunu a "paragon" and a "modern-day hero." Relating to Vanunu, Grass writes that only "heroes such as that are needed in the world, which utters words of peace while planning destruction." The poem details Vanunu's life story.

Grass describes how Vanunu was seduced and kidnapped by Israeli agents abroad, after which the former Dimona worker was charged with espionage and placed in solitary confinement for 18 years. He calls Vanunu a "righteous man, who has remained loyal to his country the entire time," comparing him to the Biblical Joseph, who was thrown into the cistern by his brothers.

Grass, who is most famous for his 1959 novel "The Tin Drum," denies he is anti-Semitic, but his moral authority has never fully recovered from his admission in 2006 that he once served in Hitler's Waffen SS.