"Iran is no longer on the offensive but on the defensive and we have to keep it on the defensive," US Under Secretary of State Nicholas Burns said at the annual conference on the Balance of Israel’s national security in the town of Herzliya, north of Tel Aviv.
"Iran has to learn how to respect the power and the will of the international community," he said.
Last month the United Nations Security Council unanimously passed its first resolution threatening concrete steps if Iran continues to develop its nuclear programme.
Burns said that "if by February 21 Iran does not suspend its nuclear activity in Natanz (its main nuclear research centre), it will face a second round of sanctions."
Although very cautious on the possibility of the US taking military action against Iran, Burns said that "we leave all options on the table, but we are seeking a diplomatic solution to these problems.
"Iran has to make a choice if it is going to work with us or against all of us in the world today… we do not seek confrontation with Iran, but Iran has to expect that our countries (the US and Israel) and other countries will defend our interests," Burns said.