The EU3, the United States, Russia and China -- the six countries backing the offer -- have said they are willing to negotiate with Iran on the incentives package only if it suspends its uranium enrichment programme.

Iran, which says it wants nuclear power only to generate electricity, has not responded to the offer and has refused to stop enriching uranium, a process that can produce fuel for atomic power plants or weapons.

A German government official gave Reuters more details of the letter, on condition of anonymity.

"It talks about how both Germany and Iran have been victims of historical developments," he said. "It also says 'we have to find a solution to the Palestinian problems and Zionism' and so on. It's rather weird," he added.

In May, Ahmadinejad sent U.S. President George W. Bush an 18-page letter discussing religious values, history and international relations.

In it, he took swipes at Israel and Washington, both of which are attacked in the letter to Merkel, the official said.

Several thousand people demonstrated in Berlin on Friday against the Israeli bombardment of Lebanon. Protesters shouted "Allahu Akbar" -- "God is Greatest" in Arabic -- and carried posters with slogans like "Israel drinks the blood of our children".