Iran passed a law on Wednesday to immediately begin enriching uranium to a level closer to weapons grade and to suspend the access of international inspectors to its nuclear facilities if sanctions are not lifted by early February, shortly after President-elect Joseph R. Biden Jr. takes office.
The law was the clearest fallout yet from the assassination of Iran’s top nuclear scientist, which Iranian officials have promised to avenge.
The law orders Iran’s atomic energy agency to begin enriching uranium to 20 percent immediately, returning Iran’s enrichment program to the level that existed before the 2015 nuclear agreement.
The enrichment order could be seen as a provocation in the waning days of the Trump administration. President Trump, who made containing Iran a main foreign policy goal of his administration, has considered attacking Iran during his lame-duck period.
The law sets a two-month deadline for oil and banking sanctions against Iran to be lifted before barring inspectors, creating a potential crisis for the early days of the Biden administration. The timing seems deliberately intended to press Mr. Biden to re-enter the nuclear deal with Iran immediately upon taking office.
The speaker of Iran’s Parliament, Mohammad Baqer Qalibaf, a former commander of the Islamic Revolutionary Guards Corps, said the measure was meant to send the West a message in the aftermath of the assassination that the “one-way game is over.”
Iran’s Parliament, dominated by conservatives, initially passed the law in an angry session on Tuesday in which lawmakers fumed over the killing of the scientist. The scientist, Mohsen Fakhrizadeh, a high-ranking official in the Defense Ministry, was killed in an ambush on Friday that intelligence officials have attributed to Israel.
“The criminal enemy will not feel remorse unless we show a fierce reaction,” Mr. Qalibaf said. Lawmakers stood up in the chamber with fists in the air, chanting “death to Israel” and “death to America” as they passed the bill.
The law was ratified by Iran’s Guardian Council, an appointed body that oversees the elected government, on Wednesday.
President Hassan Rouhani had opposed the move, calling it counterproductive.
“The government does not agree with this legislation and considers it damaging for diplomacy,” he said on Wednesday before the law was ratified.
However his government is now obliged to carry it out.
The order to enrich uranium at 20 percent would be a concern because it is considered to be close to the threshold of bomb-grade uranium, which can be as high as roughly 90 percent. Iran has said its nuclear program is for peaceful purposes though Israeli officials and some American intelligence officials believe that Iran has a secret weapons program.
Iran had limited its enrichment to under 4 percent under the nuclear agreement, which the Trump administration abandoned in 2018.
The law indicated the higher enrichment was contingent on continued sanctions against Iran, and demanded that European nations that are still party to the nuclear agreement provide relief from the American sanctions.
The law also calls for storing 120 kilograms per year of uranium enriched to 20 percent for “peaceful purposes.”
David Albright, president of the Institute for Science and International Security, a nonprofit in Washington that tracks nuclear proliferation, said that it would take Iran at least six months to convert its existing stockpile of low-enriched uranium to 20 percent.
“They know how to do it,” Mr. Albright said in an interview. “They’ve done it before. Something less than six months is the worst-case scenario if they devote all their resources to it.”
Mr. Rouhani’s top adviser, Hesameddin Ashena, said that the brief window for Mr. Biden to act after taking office could allow the hard-line faction to take credit for lifting sanctions and for getting Washington to re-enter the nuclear deal by threat instead of by diplomacy.
That would be contingent on Mr. Biden acceding to Iran’s demands.
It is also possible that the hard-line approach could alienate a new administration that had pledged to work with Iran to rebuild the nuclear agreement.
The Biden transition team did not comment on the Iranian law.
“We’ll decline to comment on this development out of respect for the principle that there is one president at a time,” said Ned Price, a spokesman.
“I think the law is a clear sign that Tehran will not be taking a “wait and see” attitude toward Biden’s Iran policy,” said Henry Rome, a senior Iran analyst at Eurasia Group. “Tehran wants to be at the top of the agenda for the new administration and escalating its nuclear program is a surefire way to do it.”
Katie Glueck and William J. Broad contributed reporting.