The Obama administration program of sanctions and diplomatic efforts to stop Iran from gaining nuclear capabilities is not working, the top U.S. commander in the Middle East told a Senate committee Tuesday, adding that Tehran has a history of denial and deceit and is “enriching uranium beyond any plausible peaceful purpose.”

Gen. James Mattis, head of U.S. Central Command, said it still may be possible to use sanctions and other pressure to bring Tehran “to its senses.” But he also warned that he believes Iran is using the ongoing negotiations to buy time.

“That should not be in any way construed as we should not try to negotiate. I still support the direction we’re taking,” Mattis told the Senate Armed Services Committee. “I’m just — I’m paid to take a rather dim view of the Iranians, frankly.”

Mattis’ blunt assessment comes amid continuing international worries and uncertainty over the purpose of Iran’s enrichment programs. Tehran denies any work on, or interest in, nuclear weapons, but international leaders believe its uranium enrichment is aimed at developing atomic weapons. The head of the U.N. nuclear agency said Monday that he can’t guarantee that Iran’s nuclear activities are peaceful unless Tehran is more cooperative and inspectors are allowed access to sites where they believe work on weapons development may be taking place.

Iran, meanwhile, has shown interest in suggestions that some sanctions might be lifted if it ships out its stockpile of material that can be turned quickly into the fissile core of a nuclear weapon and shutters the plant producing it.

The Obama administration has not ruled out military action to prevent Iran from obtaining a nuclear weapon. And, under questioning from senators, Mattis said the U.S. military has the ability to bring Iran to its knees.

“There are number of means to do that,” he said, “perhaps even short of open conflict. But certainly that’s one of the options that I have to have prepared for the president.”

Sen. Kelly Ayotte, R-N.H., asked what the U.S. needs to do to prove that it is serious that it will not accept a nuclear-armed Iran.

“I fear that if they (Iran) continue to use negotiations to delay, that we will be at a point where they have nuclear-weapons capability, and then it’s too late,” she said.

Mattis also said Iran continues to pose an increasing security threat in Syria, where the Tehran government is backing the Assad regime against opposition forces, and that Iran’s Iranian Revolutionary Guard is in the fight and bringing in other foreign fighters. Asked whether the U.S. has contingency plans to deal with the possible collapse of the regime, Mattis said there is “quiet planning” going on with other allies in the region.

He said chemical weapons sites in Syria are becoming increasingly vulnerable due to the chaos and civil war going on, even though as the fighting continues some weapons have been transferred to more secure locations.

“Our planning is taking this into account to the degree that it can. And I’ll just tell you that we have options prepared,” he said.

Mattis added that a collapse of the Assad regime would be the “biggest strategic setback for Iran in 25 years.” If that happened, Mattis said he believes Iran would arm militias inside Syria and redouble efforts in other countries such as Iraq and Yemen.

Asked about arming the rebels seeking to overthrow Assad, Mattis said he has concerns because a “significant minority” of the opposition has extremist Islamic views and some are linked to al-Qaida.

(AP)