TUNIS: US Defense Secretary Leon Panetta is acknowledging that international sanctions have not achieved their aim of compelling Iran to rein in its nuclear ambitions.    

He said Monday that sanctions are hurting Iran's economy. And he said that although the ''results are not obvious at the moment,'' Iran has at least expressed a willingness recently to engage in nuclear negotiations.

Panetta told reporters at the North Africa American Military Cemetery that the international community is still determined to stiffen the sanctions in hopes of preventing Iran from acquiring a nuclear weapon.

Panetta said the United States ''will not tolerate'' an Iran with a nuclear weapon, and he said that it is prepared to use ''all options'' to stop Tehran. Iran says it is enriching uranium for civilian energy, not military purposes.