Former New York City Mayor Rudy Giuliani says the U.S. should take a stronger stance against Iran or risk appeasing what he calls an "insane" regime.

Giuliani told a rally in Berlin organized Saturday by the exiled opposition group National Council of Resistance of Iran that anyone who thinks Iran wants nuclear power for peaceful means is "stupid."

After his speech, Giuliani told The Associated Press that he believes Shiite Iran is trying to create an empire by exerting control of Iraq and Syria. He says this could prompt a dangerous reaction from Iran's Sunni rival Saudi Arabia.

U.S. Secretary of State John Kerry has recently said Washington will endorse only an agreement with Iran that seriously and verifiably crimps Tehran's ability to make atomic arms.