Maj-Gen Jafari was writing to Hezbollah chief Hassan Nasrallah
Iran's Revolutionary Guards leader has predicted the imminent destruction of Israel by fighters from the Lebanese movement Hezbollah.
"We will soon witness the destruction of the cancerous scum of Israel at the strong, capable hands of Hezbollah," Maj-Gen Mohammad Jafari wrote.
He was writing to the group's leader Hassan Nasrallah following the killing of senior commander Imad Mughniyeh.
Iran and Hezbollah blamed Israel for the death, something Israel has denied.
Fars News Agency said Maj-Gen Jafari was writing to Mr Nasrallah to extend "congratulations and condolences for the martyrdom" of Mughniyeh, who died in a car bomb in Damascus last week.
The Hezbollah veteran was high on US and Israeli wanted lists, accused of involvement in a string of militant attacks since the 1980s.
Israeli officials declined to comment on the specific remarks.
"We are not harbouring any illusions about the Tehran regime's true intentions nor its extremist agenda," said foreign ministry spokesman Mark Regev.
Iranian President Mahmoud Ahmadinejad has often predicted the imminent demise of Israel, drawing sharp criticism from its allies in the west.
The Revolutionary Guards were set up after the 1979 Islamic revolution with a separate command structure to the regular military to protect Iran's Islamic system.
Hezbollah forces battled the Israeli army in the July 2006 war, which the Lebanese militia claims as a "divine victory".