Washington (CNN) -- Defense Secretary Robert Gates said Tuesday he believes sanctions imposed in response to Iran's nuclear development program are having more of an impact than the leadership in Tehran initially expected.
"I personally believe they're still intent on acquiring nuclear weapons, but also the information that we have is that they have been surprised by the impact of the sanctions," he told an audience of corporate leaders.
The latest "measures have really bitten much harder than they anticipated, and we even have some evidence that [Supreme Leader Ayatollah Ali] Khameini now is beginning to wonder if [President Mahmoud] Ahmadinejad is lying to him about the impact of the sanctions on the economy and whether he's getting the straight scoop in terms of how much trouble the economy really is in."
Gates said that "the only long-term solution in avoiding an Iranian nuclear weapons capability is for the Iranians to decide it's not in their interest. Everything else is a short-term solution."
The United States and other countries fear Iran wants to develop nuclear weapons technology, but Tehran denies it. Iran is now subject to four sets of U.N. sanctions, while the United States and the European Union have also imposed separate penalties on Iran over its refusal to stop enriching uranium.
Iran recently agreed to new talks about its nuclear program with the U.S. and its allies.
Last week, however, Iran's finance and economics minister brushed aside questions on the impact of the sanctions.
"Iran has faced sanctions for 30 years," said Shamseddin Hosseini, who was in Washington for International Monetary Fund meetings. "And yet Iran's economy is stronger."