Congress is moving to dramatically tighten economic sanctions against Iran as lawmakers from both major parties express impatience over U.S. efforts to halt the expansion of Iran’s nuclear program.

House and Senate officials began crafting legislation this week that congressional leaders say will deepen the pain for Iran across multiple fronts, making it even harder for Iranian businesses to buy insurance, obtain foreign financing and export goods.

The proposals, some of which could carry financial risks for U.S. allies as well, have attracted scores of Republican and Democratic sponsors, who say they will push for passage before the August recess. Supporters say the measures would build on sanctions approved last year that helped trim Iran’s oil exports by 40 percent.

“What we’ve done so far has been good, but it’s clearly not enough,” said Rep. Howard L. Berman (Calif.), the ranking Democrat on the House Foreign Affairs Committee, which is drafting a new sanctions bill. “The pressure needs to intensify.”

The search for additional leverage against Iran comes as the Obama administration announced measures intended to expand the list of Iranian companies and individuals covered by existing U.S. sanctions. Treasury Department officials on Thursday named Iran’s main oil tanker conglomerate, the National Iranian Tanker Co., to the U.S. blacklist, along with several suspected front companies and financial institutions accused of helping Iran circumvent restrictions on its oil exports.

Some of the firms are alleged to have masked the exports by repainting or reflagging oil tankers to conceal the country of origin, Treasury officials said.

The administration also tried to strike at Iran’s ongoing efforts to acquire nuclear and missile technology, listing 11 individuals and groups said to have aided those efforts.

“Iran today is under intense, multilateral sanctions pressure, and we will continue to ratchet up the pressure,” David S. Cohen, undersecretary for terrorism and financial intelligence at the Treasury Department, said in announcing the measures.

The demand for new sanctions has been building in Congress since last month, when a third round of nuclear talks between Iran and six world powers in Moscow ended with no visible progress toward a deal on reining in Tehran’s nuclear activities. White House officials had hoped that Iran would agree to concessions to head off an oil embargo and banking-sector sanctions, both of which took effect two weeks ago.

Instead, Iran has rejected demands that it shut down the most controversial parts of its nuclear program, including production of a kind of enriched uranium that can be quickly converted into weapons-grade fuel for nuclear bombs. It has refused requests from U.N. inspectors for access to military facilities that U.S. officials suspect were used to test nuclear detonators.

The stalled talks have spurred criticism of the Obama administration’s approach to the Iran crisis, leading Republicans and some Democrats to call for more assertive policies, including explicit threats of military force. Supporters of harsher measures point to the White House’s resistance to a package of sanctions that was approved by the Senate last year, in a 100 to 0 vote.

“The message from Congress to the administration was clear: Impose crippling sanctions or we will for you,” said Sen. Mark Kirk (R-Ill.), a primary sponsor of last year’s sanctions legislation, together with Sen. Robert Menendez (D-N.J.). “That message hasn’t changed, and after Moscow, that’s where we’re heading.”

The administration, which declined to comment on the new initiatives, has expressed support for tougher sanctions while cautioning against measures that could harm U.S. allies or undermine efforts to build an international consensus against Iran.

In private meetings, White House officials have warned that overly broad restrictions could prove costly for Iran’s neighbors such as Turkey and the United Arab Emirates, countries that have supported U.S. efforts to isolate Tehran.

“After a while it comes a question of ‘Who are you hurting,’ ” said a congressional aide, who spoke on the condition of anonymity to discuss private conversations with administration officials. “If you completely cut off Iran’s ability to make payments to some of its neighbors, that’s going to affect these countries’ enthusiasm for helping us further.”

Iran’s response to the sanctions has been mixed. After years of dismissing the effect of sanctions, a growing chorus of officials and lawmakers there has acknowledged serious financial harm and called for measures to prop up the country’s economy.

But Wednesday, Iran’s supreme leader, Ayatollah Ali Khamenei, reverted to rhetoric he frequently used before the recent round of nuclear talks began in April. In a speech posted on his Web site, he said Iran was “100 times stronger” today because of three decades of economic sanctions.

“These days Westerners are being sensational about sanctions,” Khamenei was quoted as saying, “but they don’t understand that they themselves vaccinated Iran through their sanctions imposed over the last 30 years.”

Iranian officials also have taken steps to limit local news accounts describing the economic toll of the sanctions. In commentary on official Iranian Web sites, the head of Iran’s Culture Ministry cautioned journalists against publishing reports contrary to the official line. “Our country is not in a position to allow the media to publish news or analysis which is not compatible with the regime’s and national interests,” the culture minister, Mohammad Hosseini, was quoted as saying.

Despite the warning, local newspapers and broadcasters have carried numerous reports highlighting the deteriorating fortunes of key industries such as petroleum and automobile manufacturing, which is down 40 percent over the past year.

“We cannot say that this situation is simply because of sanctions,” said Roohollah Beigi, a cleric and member of parliament. “A large part of the issue of high prices is due to mismanagement by the authorities.”

Rezaian reported from Tehran.