Washington ? The tough new sanctions on Iran imposed by the Bush administration Thursday come after months of frustration at the reluctance of other nations to crack down on Tehran and reflect the administration’s faith in the model of unilateral diplomacy it followed in achieving its recent nuclear deal with North Korea.

That process involved a similar designation by the Treasury Department of a bank in Macau, which froze North Korean assets and eventually led to that regime coming back to the table with the U.S. in talks over its nuclear program.

“We want diplomacy to work,” said Stuart A. Levey, undersecretary of Treasury for terrorism and financial intelligence. “But sometimes for diplomacy to work, particularly a complex diplomatic movement over several years, which is what we’re engaged in, it does need to be buttressed by sanctions.”

Thursday’s sanctions – which target Iran’s Revolutionary Guard Corps (IRGC), three of the country’s largest banks, several IRGC-affiliated companies and eight people that the administration said are engaged in missile trade – mark the first time that the United States has targeted the armed forces of any sovereign government and are considered the harshest measures since the 1979 takeover of the American Embassy in Tehran.

“These sanctions are intended to create leverage for diplomacy,” said Matthew Levitt, a senior fellow at the Washington Institute for Near East Policy who was deputy assistant secretary for intelligence and analysis at Treasury until earlier this year. “What they’re saying is, how can Iran sit down at a table with us to negotiate while doing all these things behind our back? There has to be a cost to illicit behavior, followed by an articulation of carrots.”

Some think the new sanctions also are aimed in part at persuading other members of the U.N. Security Council to impose harsher multilateral sanctions.

“Increasingly, Russia and China are more worried about the prospect of the U.S. bombing Iran than of Iran getting the bomb,” said Karim Sadjadpour, an Iran scholar at the Carnegie Endowment for International Peace.

The hope is that, as with Pyongyang, the sanctions will hurt the Iranians enough that they will be more cooperative if they come back to the negotiating table. Talks have taken place in Baghdad over Tehran’s alleged meddling in Iraq against U.S. interests, and the administration has offered to negotiate over Iran’s nuclear program on the condition that Tehran suspend its enrichment activities.

“For a regime like North Korea’s or Iran’s, for diplomacy to work, you have to have them by the throat,” said a senior administration official who spoke on condition of anonymity. “They need to have something to lose.”

Secretary of State Condoleezza Rice, who on Wednesday called Iranian policies “perhaps the single greatest challenge” to U.S. security, said in introducing the sanctions Thursday that “the Iranian government continues to spurn our offer of open negotiations, instead threatening peace and security by pursuing nuclear technologies that can lead to a nuclear weapon, building dangerous ballistic missiles, supporting Shia militants in Iraq and terrorists in Iraq, Afghanistan, Lebanon and the Palestinian territories.

“If they choose to continue down a path of confrontation, the U.S. will act with the international community to resist these threats of the Iranian regime.”

The U.S. has been pressuring the U.N. Security Council for years to impose harsher sanctions to keep Iran from developing nuclear weapons and has been frustrated by the reluctance of the Russians and Chinese to impose a third round. Such European countries as France and Germany also have long-standing commercial ties to Iran. The decision on the third round was postponed until the reports due in mid-November from the head of the U.N.’s atomic watchdog agency, Mohamed ElBaradei, and European Union foreign policy chief Javier Solana.

The first two rounds of U.N. sanctions showed that the international community was united in opposition to Iran’s pursuit of its nuclear program.

But the posture of the Iranians toward sanctions, new and old, has continued to be one of defiance.