U.S. Secretary of State Hillary Clinton and European Union foreign policy chief Catherine Ashton vowed Thursday they will keep pressuring Iran on its nuclear program, saying they won't "back down."

Clinton said Iran can still engage the international community on its nuclear program, but the offer won't be on the table forever.

"We will continue our close consultation on next steps in keeping with our dual-track approach. But let me be clear, we will not wait out and we will not back down," the chief U.S. diplomat said in a joint news conference with Ashton.

Ashton, the EU High Representative for Foreign Affairs and Security Policy, said the EU wants to have dialogue, but was disappointed so far by the outcome of such dialogues.

"We have to consider what else needs to be done and we stand ready to do that," she said.

The United States and the EU are driving forces behind the push for more sanctions on Iran, referred to as the "pressure track" in the double-track process on the Iranian nuclear issue.

Iran denies Western suspicion about its nuclear ambition, insisting the program is for civilian use only.

The United States, France, Russia, Britain, and China -- plus Germany (P5+1) on Saturday held discussions on the Iranian nuclear issue in New York, the first such meeting since Iran missed a deadline set up by the West to accept a U.N. backed uranium swap deal by the end of last year. The meeting ended with no clear agreement. U.S. State Department spokesman P.J. Crowley said the meeting was "constructive."