Khamenei's remark will be understood by Iranians to refer largely to the United States and Britain, the "Great and Little Satans" long reviled by Iran's revolutionary theocracy for their support of the Shah, overthrown in 1979.
The comment carries weight, because the conservative cleric is the ultimate arbiter of high state policy under Iran's unwieldy dual system of clerical and republican rule.
Khamenei did voice guarded appreciation of the deal, saying it was significant, and urged calm, perhaps alluding to surging popular hopes for an end to Iran's isolation, or to strains between the supporters of the deal and its critics.
But his downbeat, measured tone was in contrast to lavish praise for the agreement from pragmatic President Hassan Rouhani and his Western-educated foreign minister, Mohammad Javad Zarif.
Figures close to Khamenei lost little time in taking aim at the accord, which lifts sanctions on Tehran in return for Iran accepting long-term curbs on a nuclear program that the West has suspected was aimed at creating a nuclear bomb.
One saw worrying discrepancies between the U.S. and Iranian interpretations of what had been agreed.
"The Iranian fact-sheet of the conclusion of the deal issued by the foreign ministry had significant differences with what America's president mentioned in his remarks,” Mohammad Kazem Anbarlui wrote in an editorial for the conservative newspaper Resalat.
"The fact-sheet of the rival shows that Iranian red lines, particularly about the lifting of sanctions, have not been observed. The phrases and words used in the text contain parentheses and it is loaded with interpretable, ambiguous or multi-meaning expressions," he added.
Some conservatives believe reaching a deal with Washington is tantamount to a pact with the devil.
