The administration of President Barack Obama pushed for tougher sanctions on Iran to curb its nuclear ambitions after driving home the point that its near year-long diplomatic engagement with Tehran had yielded little.
However, it was not clear if the administration can yet rally the support it needs for a fourth round of UN sanctions when it said China is unable to join the United States, Russia, Britain, France and Germany in Brussels on Friday.
Both Russia and China, which a US official said had a scheduling problem barring it from attending the six-power meeting, have been more reluctant than the other four powers about tightening sanctions.
The group is known as the P5-plus-1, or the permanent five veto-wielding members of the UN Security Council, plus Germany.
With a year-end deadline, the administration signalled Friday that time is running out for Iran to seize its offer of diplomatic engagement for resolving nuclear and other issues.
Following up on pessimistic comments she made last week, Secretary of State Hillary Clinton said Obama's engagement policy had yielded few, if any results.
"We have reached out. We have offered the opportunity to engage in meaningful, serious discussions with our Iranian counterparts. We have joined fully in the P5-plus-1 one process. We've been at the table," Clinton said.