U.S. lawmakers have proposed tighter economic sanctions on Iran, as senior intelligence officials say measures already in place are having an effect.

Lawmakers in Washington unveiled proposals Tuesday for sanctions that would target Iran's national oil and shipping companies, and restrict its ability to tap into electronic banking services.

Tensions have risen in recent weeks since the U.S. and European Union imposed the toughest sanctions yet in a drive to force Iran to provide more information about its nuclear program. The measures aim to block crude oil sales by Iran, OPEC's second largest exporter.

CIA Director David Petraeus said Tuesday that sanctions are hurting Iran now more than ever before.

Stephen Zunes, a Mideast analyst at the University of San Francisco, told VOA the sanctions are having an economic impact, but that the political impact remains to be seen.

“If they end up hurting ordinary Iranians more than the Iranian elites, it may get people to rally around the flag and may give the regime an excuse to confront the growing popular upset at their misguided economic policies domestically. So as in any kind of sanctions — a fine line between putting pressure on the regime and creating an atmosphere where it will create the kind of popular backlash that could lead to compromise.”

Iran said Tuesday that three days of talks with inspectors from the U.N. nuclear watchdog were “constructive,” and that the two sides have agreed to continue their dialogue.

The International Atomic Energy Agency inspectors traveled to Tehran Saturday for meetings with Iranian officials about suspicions that the country's uranium enrichment program is designed to produce nuclear weapons. Iran says the effort is solely for generating electricity.

Iranian media reported the six-person IAEA team did not visit any nuclear sites, saying only “technical and legal issues were discussed.” Also Tuesday, the semi-official ISNA news agency said some hardline Iranian students had gathered in front of the country's Atomic Energy Organization to protest the inspectors' visit.

Iranian Foreign Minister Ali Akbar Salehi offered Monday to extend the IAEA visit. Iran has also said frequently in recent weeks that it is prepared to resume talks with world powers — talks which were suspended more than a year ago.

But Iranian leaders have also threatened to close the vital Strait of Hormuz shipping lanes if sanctions prevent the country from exporting crude oil. Washington has said it would not tolerate a blocking of the waterway.