But Iranian President Mahmoud Ahmadinejad said he was "not worried at all" about additional sanctions, dismissing them as ineffective.
Nicholas Burns, U.S. Undersecretary of State for Political Affairs, said China and Russia had been stalling a new United Nations Security Council resolution since late March.
The five permanent powers on the U.N. Security Council plus Germany will meet in London on Friday to weigh broader sanctions. Increased saber-rattling between Iran and Washington is stirring fears of war if diplomatic pressure fails.
Conferees agree to boost funding for Navy shipbuilding (FCS)