Geneva ? A U.S. decision to bend policy and sit down with Iran at nuclear talks fizzled Saturday, with Iran stonewalling Washington and five other world powers on their call to freeze uranium enrichment.

In response, the six gave Iran two weeks to respond to their demand, setting the stage for a new round of U.N. sanctions.

Iran’s refusal to consider suspending enrichment was an indirect slap at the United States, which had sent Undersecretary of State William Burns to the talks in hopes the first-time American presence would encourage Tehran into making concessions.