Iran and its Western counterparts returned Thursday to the negotiating table in Geneva, Switzerland, for talks on Iran's nuclear program. An interim deal in November offered Iran relief from some economic sanctions in exchange for Iranian pledges to curb nuclear research activity.
Khamenei told an audience gathered at the Iranian holy city of Qom he was wary of Washington's attitude regarding Iran.
"The enemy's smile shouldn't be taken seriously," he was quoted as saying by the semiofficial Fars News Agency.
Iran has expressed frustration with U.S. sanctions pressure exerted since the November agreement. The U.S. government, however, defended its enforcement of existing sanctions on Iran, saying it was concerned about potential proliferation issues.
U.S. State Department spokeswoman Jen Psaki said during a Wednesday press conference Washington was moving in the right direction with Iran.
"New sanctions in any capacity would undermine the prospects for a successful comprehensive nuclear agreement with Iran," she said.