Iran's Supreme Leader Ayatollah Ali Khamenei said on Friday Iran would retaliate over Western-backed oil sanctions and any threat of attack, after U.S. Defense Secretary Leon Panetta was cited as saying he feared a possible Israeli strike as early as April. Khamenei's defiant speech to mark the anniversary of the 1979 Islamic Revolution was the first direct response to tighter sanctions imposed by the West in recent weeks to force Tehran to abandon a nuclear program it says has purely peaceful ends. "Threatening Iran and attacking Iran will harm America ... Sanctions will not have any impact on our determination to continue our nuclear course ... In response to threats of oil embargo and war, we have our own threats to impose at the right time," Khamenei told worshippers in a speech broadcast live on state television. "I have no fear of saying that we will back and help any nation or group that wants to confront and fight against the Zionist regime (Israel)." U.S. media reports said U.S. Defense Secretary Panetta believed there was a growing possibility Israel would attack Iran as early as April to stop it building a nuclear bomb.