"No unmanned or manned (surveillance) aircraft have entered Iran's air space" apart from one US stealth drone that was captured last December, Brigadier General Farzad Esmaili of the Revolutionary Guards' air defence command told the official IRNA news agency.

He was reacting to a story in The Washington Post newspaper last weekend that said the Central Intelligence Agency sent its first surveillance drone over Iran three years ago with "never even a ripple" detected in Iran's air defences.

The report said CIA drones subsequently scoured dozens of sites in Iran, making hundreds of passes over suspicious facilities before the stealth drone -- an RQ-170 model -- crashed inside Iran's borders in December.

The expanded intelligence collection reinforced the view within the White House that it will have early warning of any move by Iran to assemble a nuclear bomb within its disputed nuclear activities, the report said.

But Esmaili was quoted as saying: "No surveillance unmanned aircraft has passed over Iran, and published photos were been (taken) by satellite systems."

He said "you witnessed what happened" when the captured RQ-170 tried to make its flight in December.

But while the Iranian commander insisted that US drones had been unable to fly over Iran, he asserted that "drones operated by the Guards and the (Iranian) military have flown over American ships (in the Gulf) and have taken photos of them."

"We are struck by the shameful and immoral positions taken by Gunter Grass, which are intended to delegitimise Israel and the Jewish people, and call on writers worldwide to denounce them," the head of the Hebrew Writers' Association Herzl Hakak told AFP.

"We will contact the PEN Club and the Nobel Committee. They must speak: it is not political, it's moral, because Grass is complicit in whitewashing the genocidal declarations of Iranian leaders," Hakak added.

The 84-year-old Grass, a Nobel literature prize winner, has come under attack in recent days for his poem "What must be said," in which he wrote he feared a nuclear-armed Israel "could wipe out the Iranian people" with a "first strike."

Israel has angrily denounced the poem, banning Grass from entering the Jewish state in response.

In Germany, the poem and Israel's reaction have stirred a debate, with Foreign Minister Guido Westerwelle on Sunday penning a commentary that appeared to criticise Grass, without making explicit reference to him.

"Germany has a historic responsibility for the citizens of Israel," he wrote in the Bild Am Sonntag. "To put Iran and Israel on an equal moral footing is not clever but absurd."

But there have also been rallies supporting Grass, and Germany's health minister Daniel Bahr, in an interview with daily Die Welt to appear in Tuesday's edition, calls Israel's decision to ban the author "completely exaggerated."

"I can hardly imagine that Mr. Grass has any interest in showing up in Israel," said Bahr, a member of the FDP liberal party, part of the ruling coalition, according to the newspaper.

Bahr also criticised Grass for not being open to listening to others' opinions.

It is not the first time Grass has sparked outrage. The author of the renowned anti-war novel "The Tin Drum" touched off a firestorm of controversy in 2006 when he revealed, six decades after World War II, that he had been a member of the notorious Waffen SS.