"I voted against them and I think they're terrible and I think it's going to hurt the people who are trying to overthrow [President Mahmoud] Ahmadinejad. People, when they're attacked from the outside and made to hurt, become more nationalistic," Paul said on Fox News's "On the Record" Monday night.
President Obama issued an executive order Monday calling for new sanctions against Iran and its central bank, which were included in the defense authorization bill that Obama signed into law last December.
Paul told Fox News that he believes decades of sanctions imposed on Cuba have "backfired" against the United States.
"People who don't like my foreign policy say, 'Oh, he's an isolationist.' People who put on sanctions are the isolationists," the presidential hopeful said.
Paul, a staunch fiscal conservative, has argued repeatedly on the campaign trail for a more limited U.S. military role around the world.
When pressed on what he would do about Iran given the current geopolitical climate, Paul said the United States should stop attempting to overthrow the Iranian government and allow Israel to "deal with it."
"I think what we should do is let Israel deal with it. They have hundreds of nuclear missiles. They took care of Iraq's nuclear power plant back in the '80s. I defended them for it."
The Texas congressman said monetary assistance from the United States "inadvertently" hurts Israel and constrains its ability to develop peace treaties and defend its borders.
"This idea that we have to automatically go to war and start a war against Iran, it's crazy," he added.