“The danger is that this is the first stage in an escalation that could culminate in a military confrontation between Iran and the United States, or Iran and Israel,” said Karim Sadjadpour of the Carnegie Endowment for International Peace. “The entire eight years of the Obama administration was an example of unprecedented but largely unreciprocated overtures for cooperation with Iran in the Middle East. The Iranians weren’t interested. And now, the Iranians sense the rest of the world would not line up with the Trump administration.”
The sanctions themselves are unlikely to have a significant effect on Iranian action. They strike at specific companies and arms traders from Iran to Lebanon and China. Mr. Obama took similar steps a year ago, after another Iranian missile test. But by and large, his administration tried to de-escalate tensions — and at one point even assured European banks that, under the nuclear deal, they were free to resume transactions with Iran without fear of American retaliation.
In announcing the new sanctions, the White House made clear that it planned to call out every violation, and respond. The Treasury Department took the unusual step of describing the inner workings of three networks that produce technology for Iran around the globe, in an effort to expose front companies and signal a new level of pressure on Tehran.
“The international community has been too tolerant of Iran’s bad behavior,” said Michael T. Flynn, the president’s national security adviser. “The ritual of convening a United Nations Security Council in an emergency meeting and issuing a strong statement is not enough. The Trump administration will no longer tolerate Iran’s provocations that threaten our interests.”
Kate Bauer, a former Treasury official who is now at the Washington Institute for Near East Policy, said the sanctions and the announcements surrounding it were “a way to take back the narrative, to declare that this is not a ‘post-sanctions era.’”
“By providing so much public detail about the networks that feed Iran’s missile program,” she said, “they will cause significant disruption.”
Even inside the White House it is unclear how much further, beyond sanctions, President Trump is willing to take the confrontation. While he suggested during his campaign that he might scrap the nuclear deal, which he described as a “disaster,” both his defense secretary, Jim Mattis, and his secretary of state, Rex W. Tillerson, made clear during their confirmation hearings that the world was better off with the accord, for the next decade at least, because of its prohibitions on Iran amassing enough enriched uranium or separated plutonium to manufacture even a single nuclear weapon.
The Iranians have largely complied with every provision of the deal, according to the International Atomic Energy Agency, which conducts regular inspections of the nuclear facilities. When small violations have been found, the Iranians have quickly rectified them, including by shipping fuel out of the country.
But nothing in the nuclear agreement deals with Iran’s support of Hezbollah or other terrorist groups, or its missile testing. A United Nations Security Council resolution, also negotiated in Vienna as the nuclear accord was being completed, calls on Iran to show restraint in testing, and prohibits test flights of a missile that could carry a nuclear warhead. Iran maintains that none of its missiles are designed for that purpose, though outside experts note it would be fairly easy to alter one to fit a warhead.
It is unclear exactly what Iran was testing last weekend. Its missile traveled about 600 miles before its re-entry vehicle exploded. That may have been accidental, or an intentional detonation. Reports in Germany have suggested that a cruise missile — harder to strike with missile defenses — was also launched, but American officials have not confirmed that.
But in both Washington and Tehran, the test itself was clearly less important than the symbolism of the moment. Mr. Trump wanted to demonstrate he would not tolerate even minor infractions of Iran’s commitments. For their part, the Iranians wanted to demonstrate that they would continue any activity not specifically prohibited by the nuclear accord, and would not be intimidated. On Friday, hours after the sanctions were announced, the Foreign Ministry in Tehran promised to impose “legal restrictions” on an unspecified number of American individuals and entities — in effect, a retaliatory blacklist.
Since Americans are already prohibited from doing business in Iran, it was far from clear what they had in mind.
In a statement carried on state television, the ministry said the identities of the American targets would be announced later, and that those targeted “were involved in helping and founding regional terrorist groups.”
That appeared to be a response to a part of the sanctions aimed at Iran’s support for various proxy forces in the region, including the Houthi rebels in Yemen.
A senior administration official called Iran’s moves “destabilizing.” Asked whether the administration believed Iran controlled everything that Houthi rebels were doing in Yemen, he conceded that Tehran may not make every tactical decision but said it arms and supports the rebels.
He said that the sanctions were “initial steps in response to Iranian provocative behavior.” The official spoke at a briefing for reporters under rules, set by the administration, that prohibited naming those conducting it.
Democrats did not criticize the sanctions, and even some former members of the Obama administration said they saw value in pushing back against the Iranians. But Senator Mark Warner, Democrat of Virginia, who serves on the Senate Intelligence Committee, warned against provoking Iran into further action.
“I urge the administration to bring clarity to their overall strategy towards Iran, and to refrain from ambiguous rhetoric — or provocative tweets — that will exacerbate efforts to confront those challenges.”